Sudden death of rabbit

by alison
(maidstone)

Hello
My male rabbit, less than a year old has just suddenly died.
He was quiet for about twelve hours but was eating and drinking.
He had a yellowish sticky fluid coming from his bum. I had no time to get him to the vets and he had a fit in my arms, his head was bucking backwards and he died within less than a minute. My vet was shocked at the quickness of it, and offered to do a post mortem but said she may not find the cause. I have another female house bunny who is well but I am most concerned and would like some advice please.
Can anyone help?