My puppy is 5 months old. He was chasing his tail earlier and bumped into the wall a bit (did not get hurt) but yelped, ran under the couch and has been really skittish ever since. He is also looking around like he is hearing voices and when I hold him he shakes like he is really really scared. It must me something neurological, but doesn't seem like traditional SM. He is not scratching or biting at flies or anything...just looking around like something just made a noise or poked him and is very scared. He was chasing his tail and has done this from time to time since I have had him, but not obsessively or anything like that. He was acting fine all day. This was like a light switch.

Any thoughts? We have a vet appt tomorrow morning.