Ya those bad experiences can happen from time to time. Even though I thought I had really good control over my dreams, a long time back I was having false awakenings that kept leading to other nightmares where they would be extremely vivid and I would have consciousness throughout the dream but I could not control the main part of the dream. Like people were trying to kill me and I could alter random parts of the dream and get aids to help me fight back and stuff but I couldn't escape the "negative" outcome. Sometimes I'd wake up in a false awakening like this one time when I was trying to escape this "lucid nightmare" of people trying to kill me (couldn't understand why I couldn't control it) I forced myself to wake up before getting shot by this corrupt police and ended up in another FA of someone trying to choke me to death... I kept telling myself to try to leave so I indirectly told my mind that if I kill the man I'll wake up and that's what I ended up doing lol... I actually woke up randomly in paralysis and was seeing imagery of flying demons around me even though I felt awake and was like terrorized for a while... When I finally got up I had actual tears running down my face because my mind believed it was so real and thought I was actually dying.

Long post but basically wanted to say that those bad experiences can happen from time to time to alot of us but you get past them.

Sometimes they're from your mind just randomly trailing to negative thoughts, bad control of the dream due to lack of good practice and knowledge, stress and fear or other external factors, and sometimes they just seem to happen. You also should try to go into the dreams with a positive outlook despite the fact that you may be expecting a bad dream. Expectation can lead to more of them and make sure you relax yourself and try to realize it's just a dream and nobody is really out to get you if you are lucid.

With more experience and if you stick around I'm sure you can figure out how to better avoid those, cope with them, or control them for sure. New techniques and strategies help you escape most of these bad situations or change them around to your advantage.