Anecdote: I used to sleep about 8 hours a day, but then had a long period of anxiety and depression that caused me to average about 4 hours sleep a day. This lasted for about 9 months, maybe more. During this time my brain was on constant overdrive, thinking about everything all the time, for most of that time I didn't notice any loss in alertness or clarity. I was particularly anxious about my friends and was out seeing different friends about 13 nights a fortnight. I was probably getting drunk about 3 nights a week. When I get depressed I don't really eat much, and I lost about 17% of my body weight. It was terrible, but in all this time I never got ill at all, not even a mild cold or cough. I missed the whole of winter 2015/2016 cold season, and I've got ill at least twice a year in winter for as long as I can remember. I am even ill now!<p>I was speculating the other day with a friend as to why this might be. I suggested that because I wasn't looking after my house I was pretty much sleeping in mould and I have heard anecdotally that that can have antibiotics that may have had an affect. He suggested that in extreme stress your body is less likely to overreact to a mild infection, and so maybe any infections may have much less obvious symptoms.<p>I'm pretty much better now and am attempting to sleep 7h30 a day, but it really does feel like a waste of time.