Exactly what SammieJane said.
I was actually warned about bad dreams in the third trimester by my drs and midwives. Sure enough, the past couple of nights I've had horrible dreams (normally I don't have bad dreams at all).
Dont worry, hon, it's just hormones and aprehension and all of that fun business. Yet another "joy" of pregnancy.
All I can suggest is trying not to focus on them, as the stress woulnd't help at all. I hope they pass soon for you!