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This seems like a great idea, and possibly the best way to approach this would be to have the time of disorientation be relatively brief. I've not written dream sequences ever, so I don't have any...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/23777 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
This seems like a great idea, and possibly the best way to approach this would be to have the time of disorientation be relatively brief. I've not written dream sequences ever, so I don't have any suggestions beyond making it obvious that it's a dream sequence. Possibly making what is occurring straightforward for the reader, but with signals that it isn't real. Then as the protagonist begins to wake up, the dream starts to morph into what is happening in reality, and both the character and the reader still believe they are asleep. Follow this up with something that jolts the character awake, and they will be disoriented as they will realize this isn't part of the dream, and be unsure as to how much of what they had just experienced was real and how much wasn't. However, the way to clarify what is going on would be the natural reaction of the protagonist anyway, which is _trying to find out_ what is happening. The character would not stay in a disoriented state. Particularly if battle-trained, they would first attempt to assess the situation, then try to find out as much information as possible to understand the danger they face, and how they can try to combat it. The vividness and horror of the nightmare might keep popping back into their head and causing them to be confused (for example if the nightmare involved being chased by werewolves, they might think they are currently being attacked by werewolves in reality, even if they don't exist), which would add to continuing the confusion of earlier, whilst keeping the true "what the hell is going on?" thoughts of the reader to a minimum. Then the protagonist and reader can be brought up to speed, either by Basil Exposition or their own assessment of the situation. This way no important information is lost, but you still get the feeling of skewed perception for a brief period.