Hi popcorn - just been through this with our son, At 19 mo, he refused to sleep unless we were in the room, and woke multiple times at night, expecting us to stay with him. We'd try creeping out of the room once (we thought) he was asleep. Invariably he'd hear us, and it would start all over again. Also started waking at 5 AM (was sleeping till 6-6:30 before this).
Is it possible to leave the room door open a tad? I discovered, completely by accident, that leaving the door ajar helped stop the bedtime distress. After putting my son in his cot, I went downstairs to get my newborn from hubby, so I could feed her while I sat in DS' room. I left the door slightly open, and by the time I got back upstairs he was doing his usual pre-sleep chattering, so I left him to it. He fell asleep alone, so didn't expect us to stay with him all night. The night wakings continued, but we could just settle him and leave the room.
Perhaps the door was some kind of a psychological separation, and he felt more secure/less distanced from us when it was open. More light filtering in may have helped too (blackout blinds and curtains in his room).
Lasted about 6 weeks here too, but managed to stop the pre-bed distress within a few days. The early waking took about 6 weeks to resolve too.
Hope it's short lived for you. Be interesting to hear if leaving the door open (if safe for your LO) works for you.