FTM & Sleep

How do you get your body to relax enough to sleep while baby is asleep? I cannot manage to sleep! She was up with my husband last night so I could sleep for a few hours and I could not do it. When I did get to sleep, I had a nightmare about her and woke up in a panic. Every noise she makes, I jump to see what's wrong or I'm constantly checking to see if she's ok. I'm so scared of what "could happen" that I have yet to stay a night alone with her (husband is night shift LEO).