18 mo suddenly refusing ALL sleep — CIO not working, losing it

My 18 mo was falling to sleep in his crib for 12 hours overnight and 2 hr naps no problem, until last week, a flip switched, and his sleep has completely fallen apart. Now he refuses naps entirely unless held (can’t transfer him to crib at all). At night, we've tried CIO for 2 nights -- he stood in his crib screaming for over 90 minutes, and we gave in and rocked him to sleep. Checkins without holding/rocking just make him even more upset. The *only* thing that works to get him to sleep at night is rocking him fully to sleep. If we do that, he’ll usually sleep through until ~5/6am. But getting there can take 1–2 hours.

I’m worried we’ve created a bad cycle where he cries forever → we give up → rock him. But also letting him scream that long doesn’t seem to be working either. Has anyone gone through this? Should we stick with extinction? Switch to something like the chair method? Temporarily just give in -- rock/contact naps -- and hope this is just a phase?

Also — how did you fix naps? I feel like everything is spiraling because he’s overtired.

Would really appreciate any concrete plans that worked. We’re desperate!!!!