Mature male tarantula having 'episodes' of unusual behavior

[TenebrisAvicularia]

Reviving this thread because I managed to get a picture of one of the 'episodes.'

It's got terrible quality and it's probably not helpful, but it does show his involuntary tensing. I just walked in and found him this way, and I didn't want to stress him by opening the enclosure and using the flash of my phone.

It's been happening more often lately, though he's still eating and recovers afterwards. It is definitely not grooming or regular mature T tapping. It looks very much like he can't control it.