I wanted to add something to everyone's post and your last past (the owner). As an obedience instructor, I often see the same problem or similar situation with anxiety. You should not punish your dog whatsoever. He is acting "jumpy" from an anxiety or fear and if you are to swat or scold, that only heightens the anxiety. By telling him he is ok and soothing him, babying him, you are reinforcing the behavior and he will progress in the direction.

What you need to do is one of two (several more beyond this also) things:

1) Ignore him. I know its hard, but it does not ignore nor punish the behavior.
2) Try working him through an anxiety with training. For example, if he is scared during a storm, do some commands with him. Offer him a reward after every command. This will be rewarding him for the behavior you want and are receiving, versus anxious behavior.

Best of luck.