Nightmares; who didn't have them during sleep. Topics can vary from person to person
or there might be  no topic at all only blackness for example.
Actually, nightmares feelings who didn't come out during the day or for a long time, or are
trauma's that is happening during the daytime.  Also the more stress, anger, troubles and feelings you hold in the more real the nightmare can feel.
Sometimes the people who appear actually stand for the emotions that you have even if you know the person. For example, the person is mad at you it doesn't have to be that you are mad at this person but it can be that you are mad. Someone once told me to turn the dream, I had terrible nightmares
about falling into blackness, she told me to turn around in the dream and walk back it was strange and didn't thought it would work. I told her what I thought about it, the answer I got was practice, I hear it a lot too I know it can be frustrating but indeed practice it after all the first thing we need to do.
So I did in two weeks it worked for me and since then it didn't happen anymore.
 
Actually feeling fear during the nightmare is absolutely normal, it is not all the feelings and troubles are gone but in a way it got a place in your unconsiousness to accept the situation as it is. But if the nightmares continue you didn't fully accept those feelings.
Sleeping after a nightmare seems almost impossible, so meditation and relaxing methods can help to get al least a little bit of more sleep. Indeed,  after all, the soul heals itself it is also good to write the bad dreams down, try everything to help yourself if bad dreams keep continuing.