The medications are delayed-release coated, so don't believe you'd get a near instantaneous reaction after swallowing it.
Yes, I'm aware of this, the dizziness starts few hours after taking the tablet in the morning (like 3). Just now I noticed that I've also developed conjunctivitis, still have stiff neck and low grade fever, strange sharp back pain and my left ear has started to trouble me. I read the full list of side-effects reported by mesalamine on Drugs dot com and all these are possible (though most of them are very rare 0.1 to 1% except for dizziness which is reported up to 10% cases). I also forgot to add that I've developed what seems a tachycardia and my resting HR has come up to 70-80 bpm (usually I have 45-50).
Perhaps I will back down to suppositories only for couple of days since they are far more localized.