i can honestly say that since the first time i astral projected i haven't had "strange occurances" actually i 've been trying to get BACK to doing it. a LOT has happened to me that is abnormal but it's never been from going to the astral plane.
since i was little i could see shadows, and angels and such. i've also been able to feel people's presence and break a person down to their core since i was a child. so it's something i'm used to, though i believe that it's possible for such occurances to happen to people who have never experienced such things being jumped started into the world of the paranormal/abnormal, i think it's more likely to happen to those that it's been happening to all their lives or when they were children thus they are somewhat used to it or will be able to deal with it in a semi-normal controlled way
if you don't remember anything of these events EVER happening to you, i'm sure you'll be alright. if you do, well you blocked them out for a reason and you must seriously contimplate whether or not you want to reopen that door, but it's nothing to worry about. in the astral plane and planes beyond, nothing WANTS to harm you and nothing has a desire to bring anything bad to you, just help in it's own way.
you see the astral plane is a higher vibration than this lowest plane we call the prime material plane, thus everything thing on above planes consciousness is on a higher level, if something did start to happen it could be that your on the wrong path and until you start listening to your spirit guides you will continue to be repremanded much like a parent will smack a child's hand that is doing something they shouldn't be doing.
i hope this has somewhat helped
if you have more questions or want me to go more in depth or anything of the sort don't be a stranger (IMG:style_emoticons/default/smile.gif