your body does pretty much all it's physical rest and repair processes ('stage 4') in the first 4 hours of sleep, so if you've slept for four hours, congratulations the essentials of your physical health are taken care of

the part of the sleep cycle that takes care of your brain and mental health (REM) happens later in the night, hence why waking up too early makes you brain foggy, and why it's so helpful to train yourself to wake up about the same time every morning

we are evolved to wake up several times in the night; we don't usually remember it, but worry and fixation can make us more likely to remember these

sleep under the influence of alcohol is chemically altered and not effective no matter if it helps you sleep - it's fine to have a drunken night of course but don't use alcohol as a sleep aid to 'knock yourself out', being drunk unconscious is not sleep

the best thing you can do for your sleep is follow a routine; go to bed and wake up at the same time most days, and have a 'wind down' routine, preferably including writing down whatever's on your mind to clear it before sleep

for long-term sleep improvement, it's better to wake up at your planned time regardless of sleep quality than to get a full nights' sleep

missing a night of sleep is NOT the disaster certain scaremonger-y sleep 'experts' will tell you - 'slept debt' does NOT exist and you will recover from a missed night of sleep within a few days of normal sleep

meditation is the best alternative to sleep if you're either unable to sleep or feeling the urge to nap (napping is bad for sleep!) - guided ones can help you not to fall asleep, but literally just lying there with your eyes closed and thinking about something neutral is good

acceptance is the best way to alleviate insomnia; do something else, use meditation to supplement that rest, and accept that you aren't sleeping (often, ironically, this will cause you to fall asleep)

By the coast in Cascais