Sleep fragmentation prevents you from reaching deep and REM stages where restoration happens. Causes include sleep apnoea, stress, alcohol, poor sleep environment, and inconsistent sleep timing. A regular wake time stabilises your circadian rhythm and improves sleep architecture over weeks.
Alcohol helps you fall asleep faster but significantly disrupts sleep quality in the second half of the night, reducing REM sleep. People who drink regularly often do not connect their tiredness to evening drinks consumed hours before bed.