As best as I can tell there is no symptom that is every 100% Always one or the other.Some people with IBS have the normal 24 hour rhythm of the colon disrupted, so do not get the typical "colon goes to sleep" when "person goes to sleep"But this is more common in IBD than in IBS.However, if it is a one-off thing, or only happens once in a while it is less likely to be definitive.I mean if you eat something that wasn't good (or caught a GI bug) even a compltely normal GI tract person can wake up in the night with diarrhea.Now if this is happening most nights...that is more telling.Also, I hate to say it, but your mind does interact with the nerves controlling the GI tract and if you are worried/obsessed/or otherwise emotionally stressed over being sure you have Crohn's or UC, that will make the IBS symptoms worse as well.K.