21 month old sudden sleep issues.

My son has pretty much slept through the night for about a year now. The past week or so he's been up on and off every night just screaming for a few minutes then falling back to sleep. Tonight he didn't go back to sleep so I went in and tried to soothe him. Because he's been such a great sleeper we don't really have a method for this that works well. I try to shush him and lay him back down but then he'll scream if I leave, I'll try to rock him but then he'll scream when I lay him down, I try to bring him into our bed but he won't sleep there and ends up tossing and turning. Eventually we just end up going downstairs (my husband or myself) so that the other parent can sleep, let him tire himself back out and then start over. This takes 2 hours and is exhausting on everyone. I don't know why he's waking up so often all of a sudden and I don't know how to get him back to sleep successfully. Help 😭😭😭