My sleep problem is the reverse of most. I fall asleep without warning in daytime. Fainted once recently. Someone who is excessively sleepy can have one of two problems. Either they have a condition that is disrupting their sleep at night such as sleep apnea or periodic leg movements.
Narcoleptics often have what are called sleep attacks where they fall asleep at a moment's notice.
If you truly have this significant sleepiness, you should consult a doctor about it. I have heard that will cause you to wake up in the night. Alcohol is a sedative so it will often put you to sleep. Unfortunately, it is very short acting and after 2 to 4 hours when it wears off it produces rebound stimulation and will often awaken you. That is why a nightcap often causes a person to awaken in the middle of the night.