Are six hours of sleep enough for an adult?
Six hours is less than most adults need. Adults are generally advised to get at least seven hours, with many needing around seven to nine. Age and circumstances matter, as do sleep quality and daytime alertness.
Details
Is feeling used to it enough?
You may adapt to a short schedule without noticing all its effects on concentration or mood. Chronic insufficient sleep is linked to health problems and accidents, but one short night does not mean disease is inevitable. The repeated pattern and opportunity for adequate sleep matter most.
Consider the whole day
Notice drowsiness at work or while driving, persistent reliance on stimulants and waking unrefreshed. Recommendations vary by age; teenagers generally need more sleep than adults. Time in bed is not all sleep if you spend much of it awake.
When assessment helps
Loud snoring with observed breathing pauses, or ongoing sleepiness despite adequate sleep time, warrants evaluation. Do not drive while drowsy. Record sleeping and waking times and associated problems to distinguish inadequate opportunity from a sleep disorder that may need treatment.
Related reading: How can I improve sleep, and when does insomnia need treatment?.