I'm envious of you!

I wish I had other things to work on while I let my story sit.
But actually I'm a little scared to even think of doing something else, the reason?

What if I FORGET? *gasp*

Considering you usually create a new world and some strong characters, when you move onto something else, is it easy to go back to an old project? Is it easy stepping back into your characters to write about them again? Or do you lose the flow because you left them alone for so long?

How does it work for you?