I, thank god, have never been to prison...had plenty of brushes with the law, have spent many hours in the cells & I did spend 3 months in a juvie facility when I was 14.
However, I've got many friends who have been in prison for various periods of time (one for armed robbery 5 years, one for manslaughter 8 years, five that I can think of dor dealing- between 6 months & 4 years) and there are a lot of tics and habits that I've noticed people pick up in prison:
* Jumpiness...not necessarily anxiety...more that they're always hypervigilant. Like an above poster mentioned, being skittish about pissing around other people (go piss in an alley instead of in the bar), reacting extreme badly to frights (the classic tap-on-shoulder-get-punched-in-the-face etc). Just generally defensive.
* Possessiveness...obsessively keeping track of and guarding your shit. This can vary between just being really tight with tobacco (which is pretty universal amongst people who have gone to prison) to doing stranger things like keeping ALL their food in their room as opposed to the kitchen (communal housing is the norm here). It's hard to describe, it's not selfishness, it's different...to illustrate, before my friend went down for manslaughter if you scabbed a cigarette off him he'd just give you his pouch and you'd roll a ciggie and give it back to him. When he got back from prison when you asked him for a cigarette he'd hand you a filter, then hand you a paper, then hand you a small ball of tobacco to fashion into a ciggie. He'd absolutely give you a cigarette...it wasn't that he had a problem, it was simply that he still chronically overvalued certain possessions.
* Some of them were noticably quieter when they got out...one in particular had always been a bit of a loud mouth piece of shit- just young and dumb with a hell of a lot of hiphop informed bravado. When he got back out all that bluster was gone- he could put it on for laughs, but being a loud mouth was just not in his repitoire anymore.
* Problems socialising...some of them became noticably more solitary after they got out. For instance, one guy who spent 18 month inside for growing cannabis ended up friends with the guy who worked in the library, so all he really did was read 5-7 books a week and quietly hang out with a handful of people. When he got out he lost his interest in the whole 'party people' scene, prefering instead to stay at home and read or have a few mates over for a quiet drink. Another guy developed a quite bad social phobia (much harder time in prison) and was eventually diagnosed with PTSD and actually got some good assistance...but he also never returned to the highly social party animal life that he led before.
I think it depends a great deal on your experience...correctional facilities are pretty fucking traumatic places, the best analogy I can think of is it's like being conscripted and sent off to war. It's really no wonder that a significant percentage of people come out with various PTSD-type complaints.
The main thing to bear in mind is that this is very common and a lot of the time you just need time to readjust. You've just spent a whole load of time adapting yourself to prison- it's going to take atleast as much time/effort to adapt back to the real world. If things are getting out of hand there are numerous people who specialise in dealing with these sorts of trauma related problems (as I said, if you want to label yourself, you probably are suffering from some form of PTSD/anxiety).
And because this post has made me look dodgy as hell...my hippie friend who went to prison to manslaughter...he was extremely drunk and got into an argument with an equally drunk lout in town...it should have ended with a couple of insults, but the other guy said "You wanna take this outside?" and my friend was drunk/arrogant/stupid enough to actually go out into the parking lot with him. First punch, absolute shiner to his nose...his brain hemorraged and he was dead before he hit the ground. He called the cops/ambo on himself, told them exactly what happened and plead guilty.
Years after he got out of prison he got into another fight in town- he refused to fight and let him kick the shit out of him. He's a good guy...much as I like to think I would do the same I'm not entirely sure....