Don't feel guilty - it will all come right, really it will.

Put him into his bed for a rest - with a toy he can't swallow, a hot water bottle well wrapped up so he can't get into it and chew it, and a ticking clock very nearby (to imitate his mother/siblings' heart beat.) Leave him in just fora few seconds to start with, don't go to him if he makes a noise - wait a second till he's quietened then let him out, and then lengthen the time each time you put him in there. He may just settle down anyway, but don't leave it till bedtime as he will find it strange being on his own.