My daughter was 14 months old when I had to stay overnight at hospital for operation. I've never been away from her for longer than 4 hours since she was born. It was hard for me :p But I think it is ok for her cos she slept with my husband instead, although there were some loud and long crying, she settled down in the end.
Don't worry - babies settle down much quicker then we thought :) It is the mother who suffers more (I couldn't sleep at all that night :p)