3.5 year old perfect sleeper now can’t sleep through the night

My 3.5 year old has been an exceptional sleeper since he was 9 weeks old. We did Moms on Call. Sleep trained. It worked so well. He has always loved going to bed, had no issues going to bed or saying asleep. He has slept soundly through the night from 630p-6a since. Last Wednesday, out of NOWHERE he now doesn’t want to sleep: gets sad at bedtime, says he didn’t want to sleep, doesn’t want to be alone, makeup excuses to stall, you name it. Throws a horrendous fit, screaming sobbing if we try to history him cry it out. We’ve tried flow stars, an astronaut light that plays the nebula oh the ceiling, a light up squishy dog light to hold, leaving the door open, leaving lights on. Nothing works. He has to have one of us lay with him to fall asleep. Something he has never done. On top of that, he also is barely sleeping one hour at a time without waking up in a panic. He is so sad and scared and if we’ve sneaked out, we have to come running back immediately. I cannot stress enough how atypical this behavior is. He does not say he’s scared, no mention of monsters, nightmares or anything. WHAT DO I DO?!?!?! Help me!!! I am losing it. I keep trying to stay positive and convince myself this is just a phase but holy hell.