What Could Cause A Strange Twitching In My Dog?

If your dog is twitching in its sleep like my dog Daisy used to do then she's chasing rabbits in her dreams or rounding up sheep (she was a border collie cross). That's what we always used to say when she fidgeted and twitched while asleep in front of the TV. She is perfectly healthy and showed no ill effects in her waking life then nor now as she has apparently grown out of the habit.
If it is mainly affecting your dog's head then he or she might have an ear infection and as you know they can't get their paws there to scratch it so she might be twitching to try and deal with the problem.
If your dog is also stumbling about then he or she might be suffering from a neurological condition. Another cause may be that your animal is hypoglycemic (not to be confused with hyperglycemia) which is the medical term for a state produced by a lower than normal level of blood glucose. One of the typical symptoms of hypoglycemia is shakiness or twitching. It could also be an allergic reaction to something he or she has eaten, have they had a recent change of diet or been unsupervised outside for a period of time?
Basically, if you are really concerned then the only course of action I can prescribe is to visit your local veterinary surgery and get your pooch seen to there. If it is nothing then you'll have a weight lifted off your mind but if it is something, then you are in the right place to start treatment.

My dog is 4yrs old and twitches now and  again mainly when alert and standing still does not do it when sleeping or just resting what could this be.

The same thing happened to my dog, it ended up being a spinal injury, where her first two vertebrate were not in line. Take him to the vet asap! Could be many things.

You need to get the dog to the vet. It could be a bite from another animal, it could have been hit by a vehicle if it was allowed to run around and play without supervision. But for aggression to come about for no reason, the dog is probably in quite a bit of pain.