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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.
Wishing speedy recovery