Startle reflex suddenly worse???

He's 3.5 months. And today all his naps have been filled with startles. Like 10 or so in a row. Right when he's falling asleep. If I hold him, they seem to stop. It's starting to scare me because of course I read about infantile spasms. But since he's asleep, I don't think that's what it is. He's also overtired today, he refused naps forever so could that be why.? He hasn't startled in weeks really, maybe one or two randomly. does it get worse around this time? I'm hoping it goes away altogether soon. They don't upset him and he's not crying but I'm getting worried. I plan on bringing it up next appt but just wanting some peace of mind.