We are dealing with the same thing with my 5 year old for weeks now although it feels like the last 2 years! He was the best sleeper from 6 m to 3 so we really struggled to understand this. Definitely felt at our "wits end". I think he has just started to pull out of it the last week. We tried the dream catcher, stopped ALL tv & still he would say he had images of the bad dreams stuck in his head.
I did read that this can be a window into their subconscious & can happen when they are struggling with something. I haven't found any particular thing my son is struggling with but I did have him describe each dream & together we found a way to resolve the conflict, ie. in one dream his friends & little brother were turned into those Star Wars things, bacugones sp? He's never even seen any Star Wars & hardly ever sees a commercial on tv but he did see an ad for these things. It really upset him & was very vivid of his little brother being this small ball thingy. I explained to him about the good guys in Star Wars & "the force" & we changed them back in our heads. We addressed each dream like this & each new one as it came up. Also, before bed we talk about happy things... I ask him to imagine every detail of his birthday party (even though it's months away)... just try to put happy thoughts in his head. He really enjoys this & I think it is helping, too. He's actually stayed in his bed for 2 full nights in a row! Now is brother is waking up of course, oh well!