Also be aware of any eyewear you use. Polarizing sunglasses can about blank out a display -- and in my case, my eyeglasses have Transitions lenses (referred to in old days photo grays) which make using not only camera displays difficult but also render iPad and iPhone screens almost worthless.
I'm not into Kindles but on other tablets (eg iPads) sounds a lot like a deteriorating battery issue -- there are cases in which a device experiences power problems, goes into something a recovery, then ultimately fails. I'd also go with the thought of doing a complete reset as a starting point to sort out problems. I had a years old iPhone that exhibited problems similar to yours -- it would work fine then suddenly nose dive from showing 30-40% charge to near zero and took a plug in to restart; at least in that case I was also way overdue for a technological upgrade as well.