Question: why do deep sleeps seem really short but are really long?

Jason Ellis answered on 15 Nov 2018:

Hi Eleanor – Great question. Well, all sleep should be amnestic (you should not remember being asleep) and so if you feel like you have only had a little deep sleep it may be that you can’t remember the full amount you got. The other thing is called fragmentation. Sometimes it may look like someone got a lot of deep sleep but when we look deeper into their brain activity that deep sleep is full of ‘cracks’ (for want of a better term) and these cracks make it feel short in duration