Something similar happende to my dd(who hasn't got crohns I hasten to add) She was walking back to halls at uni, felt nauseous, dizzy, arms and legs tingling, passed out and when she came round she couldn't see!!! After what prob amounted to a minute or two(although she said it felt like half an hour) she somehow managed to make contact with another student who came out and helped her back.
She got checked out with her GP(few days later) who didn't find anything abnormal with her blood pressure etc(no bloods taken though), however a couple of weeks later she went to donate blood and after testing it they wouldn't take a donation because of low iron levels.
Maybe just a coincidence but as people with crohns can have iron deficiencies it may be worth checking out your levels.