i must admit, i used codeine to knock me out (not alcohol) but that 8hrs is a myth really, for most healthy adults the amount of sleep you need varies. I function fine on 5 hrs, anymore and i feel like ive got a hangover (sorry probably a wrong analogy for you but can't think of a better word). There is a great app that calculates the optimum time when you should wake up/go to bed based on the sleep phases, 90 minutes is a basic sleep cycle, if you awaken in the middle of a cycle, you will feel groggy and tired, if you wake just at the end of your cycle, you will feel like you had a good rest.
Theres a great article on sleep here:
How Much Sleep Do We Really Need? | National Sleep Foundation
i have used sleepyti.me in the past to figure out when i should go to bed/get up:
sleepyti.me bedtime calculator