Intrusive thoughts are a pretty normal thing. Therapy is only necessary if it causes the person significant distress.

I don’t think I’ve ever dreamed of being murdered in any way.

Though memories of dreams tend to be pretty spotty unless someone wakes up during REM sleep, the “mode” of sleep where we do most of our dreaming, so there’s probably a lot of dreams that we’ve had that we just don’t remember.

searches

https://www.mattioli1885journals.com/index.php/actabiomedica/article/view/11218

In the course of their studies, medical researchers have demonstrated that about 80% patients, woken up at their Rapid Eye Movement (REM) sleep phase, can remember their own dreams, whereas, in clinical practice, young adults can remember their dreams on their awakenings only once or twice a week.

https://en.wikipedia.org/wiki/Rapid_eye_movement_sleep#cite_note-Solms_1997-42

Rapid eye movement sleep (REM) has since its discovery been closely associated with dreaming. Waking up sleepers during a REM phase is a common experimental method for obtaining dream reports; 80% of people can give some kind of dream report under these circumstances.[42]: 10, 34 [15] Sleepers awakened from REM tend to give longer, more narrative descriptions of the dreams they were experiencing, and to estimate the duration of their dreams as longer.[16][43] Lucid dreams are reported far more often in REM sleep.[44] (In fact these could be considered a hybrid state combining essential elements of REM sleep and waking consciousness.)[16] The mental events which occur during REM most commonly have dream hallmarks including narrative structure, convincingness (e.g., experiential resemblance to waking life), and incorporation of instinctual themes.[16] Sometimes, they include elements of the dreamer’s recent experience taken directly from episodic memory.[8] By one estimate, 80% of dreams occur during REM.[45]