Swelling in neck

Sun afternoon i was bathing my Peke with Malesab shampoo and he started acting unusual then his neck started swelling.He was acting very off balance and his color was getting pale.I immediatley gave him a tsp of Benadryl ,he weighs 12.6lbs.I rushed  him to the E.R. trying to keep him alert.When we arrived the swelling had decreased maybe 20%.It looked as if a baseball was under his skin right below his ears.Also it looked like a Charlie horse half way around his head.The Dr on call wanted to send him on to U.T. in Knoxville for surgery right away.She said that he had a ruptured disc in his neck.She also detected a grade 4 heart murmur.An hour later there was a shift change ,The next Dr said that since he was walking around and the swelling was subsiding that we could wait and see my regular vet the following day.His x-ray showed narrowing of the C2  C3 area.She heard a grade 2 1/2 to 3 murmur.I brought him home the following morning,He was still a little swollen,But acting normal.His regular Dr and another Dr in the clinic could not detect any murmur,So there was no need for any EKG or ultrasound.Also the swelling in his neck had almost completley subsided.There was no ruptured disc at all. But at the time he was showing all the signs by the physical exam  and x-ray of a ruptured disc.I am really confused at the sudden onset of all of this.I dont understand how he could have gotten like that and then it all be fine.The Dr.s said that it wasnt due to the Malesab bath. I lost my 7 year old little girl Peke, Chloe 14  weeks ago and i am worried.I am still having a hard time dealing with the loss of her.My Question is,What could have caused all of this.Also how can there be a murmur detected and then it be gone.Can  extreme pain  be the cause of that?Any opinions would be nice?

[Jaybay]

You two certainly have been put through the mill.  I applaud your quick work with the benadryl.  Judging by the sudden onsetand apparent response to the benadryl, it sounds like an allergic reaction to something - what exactly I have no idea.  You'll probably never know what caused the swelling, but if it were me and my dogs I would't be using that shampoo again.  

Experiences like yours can put people off believing any medical advice - whether for humans or animals.  That was ridiculous!  I hope he's doing OK now with no other symptoms.