Tingling/numbness in hands

At night when I was sleeping my hands and arms started going numb, mostly my left. Now I try to be more conscious of the position my arms are in when I go to sleep which seems to help but I've been having a lot of tingling in my fingers on my left hand. It sort of comes and goes and doesn't seem to happen only when I'm in a certain position for to long. Sometimes it's starts as soon as I sit down. Anyone else experienced this before??