Hi friend,
Welcome to Health Care Magic
If it is happening daily, subconscious
anxiety is most likely.
Anxious to get up at a given time makes the sleep shallow, less relaxed - despite setting an alarm...
If it is an occasional event, dreams /
nightmares may be responsible.
Biological clock is unlikely to do this.
If it is disturbing and interferes with daytime activity, you may investigate -
Holter monitor / sleep lab will help.
Take care
Wishing speedy recovery
God bless
Good luck