I accidentally cut down my sleep, help ?

I usually sleep around 7.5 hours every night. While studying for a recent exam, I had been getting up in 5 hours totally refreshed and unable to get back to sleep. The exam has passed, it's been 10 days and I'm still getting up in 5 hours with no alarm clock and no effects of sleep deprivation, even on weekends.i sleep at the same time every night. I'm not trying to sleep for 5 hours on purpose.

Is this normal ? Am I hurting myself somehow ?

25 Female. Otherwise very healthy and physically active, no medications. https://en.wikipedia.org/wiki/Sleep_deprivation