18 mth old English Bulldog - biting

Question
Unfortunately me 18 mth old english bully has bitten my husband - I'm very concerned because this is out of character behaviour.  He is normally very placid and sweet though abnormally afraid of loud noises, other pets, etc. He was recently checked by the vet for tremors as suggested by your experts - he has not done this recently - and he had his anal glands emptied.  Since castration, 3 months ago he has seemed irritated by his back end and when he bit my husband it was when he touched his back end (his foot fell on it off the sofa where he was lying).  Can dogs suddently turn and is there a chance he will bite again, I have two teenage daughters and will not risk them being bitten - he seems to know his place in the 'pack' though he has started jumping up  more recently.

Any help appreciated
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The text above is a follow-up to ...

-----Question-----
Hi,

My 18 month old Bulldog who had been with us for 6 months and was previously owned by my mother in law has started an odd behaviour. He looks at you and his head shakes from side to side, he sometimes shakes from head to foot aswell.  He's quite a timid dog, very obedient for us.  He is also quite nippy when my husband plays with him.  We have teenage children and he appears to know his rank in the pack.  He has been castrated due to an undescended testicle.  

Thanks
-----Answer-----
I don't think his social behavior has anything at all to do with this physical symptoms.

I do however think something neurological is going on with the tremors. I've seen this occur with an allergic reaction to a food or substance. Think about what has gone on or what he has eaten when these occur and see if there is a connection.

Bulldogs are also prone to spinal malformations which can often put pressure on the spinal cord and cause either tremors or paralysis, temporary or permanent.

First thing to do is determine, if you can, if there's a link to something he's done or eaten that may be setting off the tremors. If you can't seem to establish a link, then I would take him to the vet for a workup.

Answer
Your dog sounds like he lacks socialization and self confidence. Why don't you take him to an obedience class just for the fun of it?  

Honestly, I can almost justify the bite because it obviously startled him and he reacted without thinking.  I always give the dog the benefit of the doubt the first time. If this is totally out of character for him, chances are it won't happen again.

However, the dog needs to feel comfortable in his own home. By that, I mean he needs not to feel threatened by other pets or frightened by normal household noises.  Get him out and about more in an effort to "desensitize" him.

You're going to have to put some effort into this for everyone's sake.