Sleeping Alone

So this dilemma we are currently facing is something we have not had to face as parents with the other three; the reason is because they have never been alone at this age during sleep. I read that some children right before or after turning two all of a sudden hate falling asleep when alone.  For almost a week now, Ian screams when we lay him down which has never been a problem for him.  If I however sit in his room he falls right to sleep (way faster at nap time).  Even though it's a beautiful picture I see, I'm tired of waiting around for my toddler to fall asleep.  I hope this is a short stage, otherwise we will be switching him and Elyse's rooms a lot sooner than planned.