I usually sleep 4 to 5 hours only. My perspective about sleep is a little different. I think that sleep patterns differ person to person. A person might feel as usual with a 5 hours of sleep. Whereas another person would need an 8 to 9 hours of sleep to feel energetic enough to go about working.

I associate sleep patterns with habit. Sleeping more or less is just another habit. If you've always been sleeping for 8 hours daily, your body will be reluctant to get up before you take a full 8 hours of sleep.

For me, it's always been 4 to 5 hours and till now I haven't felt any problems physically or mentally. I'm in my late 40s now.