I think that it is because I'm just worn out from a whole day of fighting and grappling with the pain. My body knows what I've been thru all day, even if I've been able to block it by getting involved with something to take my mind off of my PN problems for minutes or even hours at work. By the time nighttime rolls around I think my body has had it, and complains when I try to sleep. I have tried the biofreeze, Icy Hot, feet in epsom salt solution, feet out of covers, whole body on top of sheet or covers, etc. I think that I finally sleep when my body just shuts down. A few shots of vodka sometimes helps to make me sleepy, too - but sometimes I pay for it in the a.m. by waking to worse than normal(ly?). If you can call waking to burning and pain, daily...normal.
I put Icy Hot on my feet every morning to just get me downstairs to my 200mg. Lyrica & 100mg. tramadol a.m. dose (1 of 3 every day- sometimes an extra 100 tramadol in the middle of the day) Also, having emphysema (smoking cigarettes for over 50 years) doesn't make climbing stairs any easier.