Suddenly Agressive dog

Question
Hi i have a 3 yr old chihuahua x jack russell.  He is always friendly and happy, but recently he has been very agressive and even biting friends and myself and my partner.  He will be fine and then suddenly become very withdrawn and vicious.. I was wondering why this would be?  could it be becaus we are looking after 2 other dogs even though he gets along fine with them?

Answer
It would be extremely difficult for me to analyze your situation and give advice without being able to see first-hand how the dog was behaving.

If the situation corrects itself after the dogs leave, then I would say they might be the reason for his change in behavior.  If it continues, you may wish to enlist the help of a trainer who can come to your home.