yea i used that shampoo with him about 5 times before this he did fine all the other times. I had never seen him with a wet bottom before though, the whole thing was just so weird.
That seems too quick for aspiration pneumonia. Have you used that shampoo before? (I'm wondering if it was an allergic reaction) Then again, the wet bottom may have been a signal the bunny was already feeling sick and the bath was too much stress. You said the bunny seemed tired. Just thinking out loud. . . .
I am so sorry about the loss of your pet!
Unfortunately, only a post-mortem exam could give you a definitive diagnosis as to the cause of death, but I will try to speculate.
I assume your rabbit was male?
Your rabbits wet bottom may be a clue to a cause of death. Rabbits can get urinary tract infections and urinary stones. Rabbits urinate large amounts of calcium. A rabbits body can form stones from the calcium that is held in the bladder prior to urination. If the stones become large enough they can block the urethra, similar to the kind of blockage that occurs in male cats. This kind of blockage can cause death within 24 hours if not relieved.
Another possibility is gastrointestinal obstruction by a hairball. Hairballs in rabbits can also be deadly due to stasis of the digestive tract. Usually the rabbit affected by an obstruction will show more symptoms then you describe.
The symptoms or urethra blockage are vague, but urinating inappropriately can be a symptom.