My sister used to have them around the time she was three or four . I’m six years older than she is so I remember them vividly. They are very different from regular nightmares. She would ask sleep walk - get out of bed and be upset about or searching for “something” and as much as you speak to her she doesn’t Really “hear” you and if we tried to stop her or hug her she’d get even more agitated. We would just let her search and walk with her and be reassuring.. eventually she would calm down and allow herself to be led back to bed and settle down.