Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for your Chihuahua; I'm certain that this must have been somewhat distressing for you both!
Several possible explanations for his behavior come to mind:
1. Rather than a full blown seizure episode, he could have had a partial seizure. These dogs don't lose consciousness but can often experience very short, transient episodes where they stare off into space or a certain part of the body might twitch or they can't move. These episodes only last for a very short period of time though and then the patient is normal.
If this is the case, then he may have additional episodes in the future.
2. He may have had a something similar to a pinched nerve in a human. I wouldn't expect him to have repeated episodes if this were the problem.
3. I suppose some sort of cardiovascular event such as low blood pressure might explain his behavior but typically the episodes last a little longer than what you saw.
In any event, at this point, I'd continue to monitor him for re-occurrence of the behavior; if it happens again, then a vet visit might be prudent for a thorough exam and perhaps blood work to evaluate his liver and blood sugar levels.
I hope this helps and that this was just a one time event. Deb