This is a close up of the yellowing.

Hi, thanks jerrycan for pointers, however, the leaves do not 'drop off', they only break off if forced to come back up to a horizontal position. I have the plant sitting on a pebble tray for humidity and I always ensure that the soil is consistently moist, not muddy. Could it be an issue with the water itself...I live in a rural area and have well water which is UV shocked, then filtered before reaching a faucet, and I try to make sure that the water has sat out for 24 hours before using it. All but the bottom 4 leaves still display normal prayer plant behavior, folding at night and opening in the day, although I believe that I briefly had it positioned where it received too much sun, as the colored spots on the leaves changed from brown to dark green, but I understand that this also occurs as the leaves mature. Any thoughts on the artificial lighting set-up?

This is bringing tears to my eyes. I knew when I read Jane's post that something wasn't right. Luvs, thanks so much for letting us know Dear Dad went to be with his Savior. Karen, you should be a very proud daughter for the way you cared for your Dad. You will always miss him but have so many beautiful memories with him. Thanks so much for sharing your DD with all of us while he was with you. Please give his little dog lots of Hugs and Kisses from all of us too. Those we love don't go away, They walk beside us every day, Unseen, unheard, but always near, Still loved, still missed and very dear. Sharing Your Sorrow and Sending My Love, Punk

Sadly there's not a lot of heat outside here, haha. By damaged: do you mean dead leaves or also the very dried out ones that won't unfold? Also! It now has a second healthyish leaf! One of the old leaves unfolded and got a healthy colour. It still has white spots though. I changed its location to a table with a lot of sun on which my other prayer plant was doing really well. But hey, the other plant didn't go a month without water...