I'd say it's, as in most cases, a question of dosage, tolerance so on. My opinion however is that you will wake up by the laryngospasm (involuntary closing of the air-way) that many people experience when fluids enter the trachea, and the rush of adrenaline/panic this will cause.
In fact many people that drown do so with no, or very little, water in their lungs, due to this reaction. This of course is individual.
Depending on level of cns impairment however you will not need the water at all as you will drown in your own vomit, or respiratory depression, or both. Might be hard to achieve with just benzos and vodka, and as you already have tolerance I'd find it unlikely. However people die this way all the time from alcohol alone and combined with say a opiate like heroine it's know as the "rockstar death"
Effexor(venalfaxine) is a different story though but from what I remember reading you don't want to go that way. Google is your friend.