Is insomnia a side effect of some antacids?

Generally not. Antacids such as tums, maalox, mylanta certainly should cause difficulty sleeping. Stronger ones, ranitidine, pepcid, generally should either. Even stronger--aciphex, nexium, (esomeprazole) protonix--generally don't. Stronger yet--dexilant--not likely. However, the interaction of drug and each organism is different, and any drug could pretty much cause most side effects in some people.