I think the second most important thing after not making it a "cool scene is happening! then the character woke up" sequence, is still focusing on the dreamlike. Even big trauma might get jumbled by the brain during a dream, so while it feels exactly the way the events happened originally, don't go into the pitfall of making it an elaborate flashback sequence. Maybe everything moves too quickly and like an abridged version (which focuses on the worst of that event, like they're teleporting around a horror show), or it's filled with symbolism and the reader only gains knowledge of the meat of things, but is left wondering about who is involved or how it came to be.
I've got a fresh memory in my mind of a really nice, short dream sequence from a kids' book series I've been reading recently. The character is passing through a really stressful situation caused by a neutral person, who has brought nothing but confusion, threats and demands.
The dream sequence afterwards is quick but speaks more about their feelings more than having a monologue explain - a dangerous location covered in mist, with the character feeling lost, and before them stands a masked figure that they can't unveil or guess any intent. They can't keep going without crossing paths with the figure, and that's where the dream ends.
It's just a paragraph so it wouldn't be applicable here, but I think the sentiment is worth bringing up. It starts suddenly like a real dream, we're never given any description of the place or why is the character lost, but you get it with very little given, through symbolism and the anticipation that these actions bring out. The character doesn't get to the end of the dream because they haven't figured out the solution themselves, and that's what the waking world will have next.