I've never been able to nap - but a friend of mine says that 20 minutes is the optimum - more than that & it makes you feel worse

I am the same, although I find it very difficult to drop off to sleep in the afternoon anyway. I generally go to bed by midnight and find no difficulty in sleeping through until 9.00 am or even later - I reckon I'm still catching up on sleep deprivation after years of having my alarm set for 5.30 am!

Yes I've heard that too. I've tried it and does seem to work. I often doze of after lunch for about 15 minutes and feel a lot better for it.

I think its a matter of what the body is used to and looks upon as a normal timetable.

I began taking Siestas as a necessity in the UK, because I often had to work much of the night as well as most of the day.
It was slightly upsetting at first, but for a great many years now it has been the norm and the one to two hours afternoon sleep now leaves me even more refreshed than the night time sleep and the added bonus is that I have more active hours out of the 24 than I used to have with only the night sleep.

I reckon old Churchill had it right.

I used to work 4hrs on 4hrs off over a 24hr period, then get 24hrs off. When you have worked this for several months the pattern sets in but it takes time.
The worst shift pattern I worked was 8hrs on 4hrs off, 4hrs on 8hrs off, which even after 3 months was difficult to settle into.

I usually found it difficult to sleep much longer than a couple of hrs in the afternoon, especially if I was due on shift at 4pm, couldnt settle.

Even now I rarely sleep much longer than 4hrs at a stretch at night.