I remember my friend mentioned to me she might have a mutation in the DEC2 gene (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2884988/ https://www.ncbi.nlm.nih.

I remember my friend mentioned to me she might have a mutation in the DEC2 gene (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2884988/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2884988/) because she usually goes to bed around 2 am and wakes up at 6-7 am, and has been doing it throughout her life. And she says she's fine and like you doesn't feel tired if she only gets 4-5 hours of sleep. Interestingly, if she gets the standard number of hours of rest (say, 7-8), she gets really groggy and it totally disrupts her ability to function throughout the day!