Spooked Cat

My oldest cat whos 2 and a bit has been acting weird intermitantly for some time now.... it all started when i went out of town for a few weeks.... My parents & sisters where looking after the 2 cats at their place while I was away. Onyx was familiar with all my family met them many times seemed comfortable with them all. Since I've been back I've noticed his behaviour to be slightly odd... At random times he simply acts like he's seen a ghost or something... he gets real freaked out when approaching the back door to go outside. Sometimes he won't go outside for days on end... which is very strange cos he used to be a real pain if he wasn't let outside on demand. Often he'll come bolting inside for no apparent reason like he's just seen the ghost and starts creeping round the house acting very skittish...
On other days there is no problem at all can't wait to get out doesn't see ghosts and acts like "normal"
He's appears to be the leader of the threesome in this house, has had the chop and is vaccinated and all that. The cats and I now reside in the top floor of my parents house which is where the cats went too when I went out of town. Any ideas???

The first thing I would do is take him to the vet for a checkup. Sometimes these personality changes are due to an illness of sorts. If all checks out, I would guess that something happened while you were gone. He may have missed you, and that upset him. Something could have scared him, and now he's trying to deal with it. Like I said, I would take him to the vet, and if all checks out okay, give him some time to get back into his normal routine.

I wasn't quite sure by your post - you went out of town and your cat stayed at your parents, then you moved there also?
I'm wondering if he could have been frightened by something there while you were away, or if there are smells from other animals inside or out, or even if he's still just a little jittery from the move?
Things to think about after you eliminate any physical problems with a vet trip. Any other changes - like you changing your schedule, litter box in new place being in a more public area etc?

If your cat is suddenly afraid to go outside, there may be a cat or other animal that frightens him hanging around. My cat has recently sometimes refused to go out, and when I look around I usually discover a big tomcat that's new to the neighborhood lurking around our house. My mother had the same problem with one of her cats, and discovered that a skunk had decided to nest under the deck. In addition to the move, something like that would unnerve many cats.