Most times, what we think about before we get to sleep comes to us as a dream. When we worry a lot about certain conditions, the thoughts go with us while sleeping too. However, thinking isn't so good for the health, especially of you are TTC, as it is a form of stress which could tamper with with the hormones in your body.
If you will feel the thoughts and dreams are worrisome, please see a counselor. I'm sure he or she would talk things through with you.