Polypterus is correct, this behavior is NOT normal. even though a gar will knock itself out sometimes, that behavior is not normal either. there is going to be some external stimuli to cause the gar to freak out and knock itself out.
with the twitching, there is obviously something going on in the tank that has not yet been figured out. providing us with the information polypterus requested will help get to the potential causes of the problem.
keeping a skittish fish like a gar with pbass is definitely not recommended, as the pbass could easily set off the gar.
what are the tank parameters...water temp, pH, all tankmates, filtration, etc?
at least in the pond it should be calmer. keep us posted and good luck regardless--
--solomon