Our passuk, ולנערה לא תעשה דבר אין לנערה חטא מוות כי כאשר יקום איש על ריעהו ורצחו נפש כן הדבר הזה, tells us that a person who is forced by threat of death to engage in prohibited intimate relations is absolutely innocent. This is the source of the din of Oneis in its simplest application, that a person is only liable for his act when it is done willingly, but not when he was forced to do what he did. Oneis has come to include physical or mental coercion, absence of conscious awareness of the act, and reliance on Halachic Instruction. In all such cases, the act is not attributed to the actor: as Reb Yochanan says (Yerushalmi Gittin 7:6), אונסא כמאן דלא עבד, Oneis is as if this person had not done it at all. The last example, reliance on Halachic Instruction, means that if a person was told to do a certain act because it is a mitzvah, despite certain halachic risks, he is totally innocent even if the action results in unwanted consequences (Noda BeYehuda YD II 96 ד"ה והנה about yotzei l'derech samuch l'vestah.) This falls under this rubric in the sense that his act was not by his own volition: he was ordered to not be concerned about possible consequences.
So what's the halacha if a person did aveiros when he was drunk? Is he liable or not? (In Hebrew, there are two words for drunk: Shikor, שיכור, and Shasui, שתוי. In English, there are around twenty five commonly used words for it. One is 'crapulous,' which actually comes from the Latin crapula, from Greek kraipale- which meant hangover, or drunken headache- but the Romans used it for drunkenness itself.)
Let's postulate that this person is so drunk that he is no more aware of his circumstances than a Shotteh, a mentally deficient person. As the Rashba says (Toras Habayis 1:1), כל שנתבלבלה דעתו מחמת שכרותו הרי הוא לשעתו כשוטה עד שיסור יינו. We call this "Shikruso shel Lot," as drunk as was Avraham's nephew Lot when his daughters cohabited with him. Lot was so drunk that he did not even consciously realize it when his daughter came and lied down with him. (Interesting, though, because the Gemara (Nazir 23a, תנא משום רבי יוסי בר רב חוני למה נקוד על וי"ו ובקומה של בכירה לומר שבשכבה לא ידע אבל בקומה ידע ומאי הוה ליה למיעבד מאי דהוה הוה נפקא מינה דלפניא אחרינא לא איבעי למישתי חמרא) says that the next day he did realize what had happened, which is not the extreme drunkenness where the person never realizes what had happened.)
The answer to the question is obvious where it involves nezikin liability for damages to property or person. We hold that even Oneis is liable for such things. There is a machlokes Rishonim whether an absolute Oneis is liable. The Rambam (6 Chovel U'Mazik 1, and see Lechem Mishna there,) and the Ramban (Bava Metzia 82:1) hold that Oneis Gamur is liable. Even according to the rishonim (Tosfos Bava Kamma 27b and Rosh there) that Oneis Gamur is not liable for torts, a drunk would be liable, because he willingly got drunk. For nezikin, that's enough to make him liable, as indicated in Tosfos there. As far as business dealings, the halacha (CM 235:22 is that drunkenness renders all transactions null and void. But what of non-monetary issues?
Would drinking to excess be called contributory negligence such as to impute responsibility for his drunken behavior?
In one perplexing teshuva, the Ma'aseh Avraham, a famous poseik of the early eighteen hundreds in Izmir/Smyrna, Turkey, says that a suicide of an intoxicated person is treated like any other suicide and the person may not be mourned and is not buried among other Jews. Strangely, he proves his point from the halacha that a drunk is liable for civil damages, such liability stemming from having willingly becoming drunk. The Sdei Chemed brings this down and respectfully says that with all due respect, this is incomprehensible, because civil liability and guilt are completely different, as he proves from the Gemara in Eiruvin (end of 64b).
The actions of a person that is as drunk as Lot are not legally meaningful; his business transactions are null and void and he is not punished for any religious transgressions that he does while drunk. If he is not so extremely drunk, his transactions are valid and he is liable for religious transgressions.
The Rambam in 1 Nezirus 12 says:
See also שו"ת הרא"ם סי' ע"ב .
But what of the argument that a person should be liable for anything he does while he's drunk because he knew that drinking would make him insensate, and that he might do all sorts of terrible things in that state? Shouldn't a person be responsible for making himself irresponsible? Certainly, there is some guilt, but generally one assumes that this is only of a dinei shamayim level. As the Yam Shel Shlomo says (Bava Kamma 3:3), מקבל את דינו בידי שמים על מה שלא עצר ברוחו ושיכר עצמו להשתגע.
This seems to be the subtext in the Gemara in Nazir: The Gemara (Nazir 23a,) discussing the drunkenness of Lot, says that he bore responsibility for the second night, though not for the first.
The Kli Chemda (Behar 25:46) brings from his Rebbi, the Yeshuas Yisrael, a stira in a Rivash. The Rivash in one teshuva says that if a person swore a certain oath, and he knows that going to a certain place will result in being forced by threat of death to transgress the oath, he is not liable. In another teshuva, the Rivash says that if a person does not run away from a city where he knows he will be forced to do an issur of arayos, he is liable when is in fact forced to do the issur. The Yeshuas Yisrael distinguishes between general oneis and the the issurim chamurim. In the first case, where Oneis is muttar 100%, then placing one's self in a position of later oneis is not liable. But in the case of the chamuros, Avoda Zara and Gilui Arayos, where one is really obligated to be a martyr, but if he is weak, he is still not liable for the sin per se, in that case, placing one's self in a matzav of oneis is chayav. The Kli Chemda suggests an alternative pshat; that if placing yourself in that position is inherently innocuous, then you are not liable. If the act itself is assur for any other reason, then you lose the later petur of oneis. This also explains Esther's כאשר אבדתי as explained in Megilla 15a, שבכל יום ויום עד עכשיו באונס ועכשיו ברצון וכאשר אבדתי אבדתי כשם שאבדתי מבית אבא כך אובד ממך, because even going there wasn't the arayos, it just put her in a matzav where she'd be anusah on arayos.)
And this brings us to the machlokes Baal Hamaor and Ramban that I'm surprised the Kli Chemda didn't mention. In the old days, a child needed hot water after a bris, and this need was considered a matter of life or death. Water was supposed to be prepared before Shabbos if you were planning a bris. What if the water spilled before the bris? Can you do the bris, because when you'll need the water it'll be muttar to heat it because of Pikuach Nefesh? Or do you not allow the bris because you know that this will generate a situation of Pikuach Nefesh. Similarly, if a person gets on a boat on Thursday, knowing that come Shabbos he's going to have to be mechalleil because of Pikuach Nefesh. Ramban brought by Ran Shabbos 52- go ahead and make the bris. Baal Hamaor- Assur to make the bris. (Reb Shlomo Zalman Auerbach (Minchas Shlomo 7:2) holds that the Baal Hamaor means Miderabanan, and certainly once you've put yourself into this position you can do the chillul, but it's very possible to disagree with RSZ and say that you were over a deoraysa of chillul even though you're now obligated to be mechallel. For example, see the Netziv on the She'iltos in Vayeira 10:9 in the numbers of the העמק שאלה.) I really don't know why the aforementioned geonim didn't bring in the Baal Hamaor and the Ramban. You might disagree with my tzushtel to Shikrus, but they certainly are directly connected to the Rivash. But I didn't see the Rivash inside.
Accordingly, if a person knows that he might sin while drunk, and he gets drunk anyway, his liability should depend on the teirutzim of the Yeshuas Yisrael (only liable for Avoda Zara and Gilui Arayos) and the Kli Chemda (not chayav at all, because simply getting drunk is 100% muttar,) and the Baal Hamaor (chayav) and the Ramban (pattur.)
Additionally, we might bring a raya from the Agudah's opinion (brought in בית יוסף חו"מ סי' ר"ז and Reb Akiva Eiger in CM 108 and the Ketzos and Nesivos in 55) on אונס ביום אחרון. The opinion of the Aguda is that if a person had thirty days in which to fulfill a condition by doing something, and he delays until the last day, and on the last day an unforeseeable event makes it impossible to fulfill the condition, it is NOT called an oneis. He could have avoided the problem by taking care of it during the first twenty nine days: it's only because he waited till the last day that the oneis caused a problem. This, says the Agudah, is not called Oneis. The Nimukei Yosef (Bava Basra 31a by Shuka Bara'i) disagrees and holds that it is called an Oneis. It seems to me that if Oneis b'Yom Achron is not called Oneis because the person's conscious choice of inactivity contributed to the effect of the Oneis, then certainly the conscious choice of getting drunk, which increases the likelihood of an Oneis, would be the same as Yom Achron, and depend on the machlokes Agudah and Nimukei Yosef.
This is getting too long for the internet.