Hello Ned,
I have a 5 year old Ancistus Pleco who is having spasms of some sort in the last 3 weeks from time to time...he stays on the bottom when he does this. and then he's normal and hides.....Once in a great while he will swim erratically around the tank but this happen only twice. Not sure if this is a mating thing or not. Or maybe a neurological problem.
Thanks