This hasn't happened to my husband, at least not in this way. But it reminds me of a story: A wife finds her husband giving their baby a bath while leaving the bathroom window open and comes unglued! The baby was fine. No cold, no fever, just fine. Someone listening to the complaining said: at least your husband was GIVING your baby a bath!
Sometimes we focus on one thing and forget the other half of the story. You two might explore ways your husband can alter how he responds when your son overreacts.
One thing I have learned is that 3-year-olds often don't know how exactly to say what they are feeling. So, for instance, hearing my son say "it's not fair!", I would say "hmmm, sounds like (often it is "looks like ...") you are upset. Do you want to draw me a picture?" My kids didn't have the vocabulary at the age of 3 to tell me whether they felt tired, had a bruise, or understand that some joking (and playing) is for fun and pretend -- not for real.
I would encourage you to play with them a couple of times and look for what it might be that your son is trying to express.
I have caught myself telling my boys (a 15-yr-old, 10-yr-old, and 7-yr-old (oh, and the 50-yr-old! LOL) "well, I don't see any blood and you sure are scaring me screaming like you fell down, please calm down and tell me what happened" or even "oh my, maybe I need to take you to the doctor and tell him you need a shot of medicine to make it all better" (I have to contain my laugh at their reaction that, oh, it's not that bad LOL)
The comment about repeating this as something your son has heard someone else say (someone at daycare or on TV) caught my eye. I've had to explain (just a couple of years ago) "remember, you are not SpongeBob (whatever) and you don't have to act like him. You're a real boy who can talk in a regular (calm) voice about what happened."
Anyway, I'm not sure I actually told you anything helpful. Take what makes sense to you and leave the rest as rambling!
Good luck!