I would probably call nurses on call (or your state equiv) if I was concerned, just in case. It sounds like he is just not feeling well for some reason- maybe a little bug, maybe teething pain. Is he still having his breastmilk/bottles like normal? My dr's mantra about kids under 1 is that as long as they are still on their food, nothing too terrible can be wrong with them. If he's still feeding ok, I wouldn't be too concerned- just give him lots of cuddles and keep up the fluids. When DS is sick, I often feed him one of the baby jellies in jars which are mainly water anyhow.