HELP! My toddler won’t let me leave the room!

My boy is now 17 months old and he had been so independent and good at sleeping up until a few weeks ago! 

Everytime I leave the room he screams and has a meltdown! he used to be fine if I popped out to the toilet or to get something, he would just keep playing. 

then there’s bed time, normally we would do our bedtime routine put him in his cot and he would get himself to Sleep without any trouble now we cant Leave the room until he’s asleep! It’s Awful. We’ve tried everyone from sitting with him for over an hour.. controlled crying.. music.. light shows. But nothing works unless we sit there for a long time constantly lying him back down!! 

Has anyone got any tips or at least can tell me if their child’s done this and got passed it!?