Gas leak from the cooker in the caravan?
Could be that. My parents brought a new caravan about 4 years ago now time to time the fridge gives off fumes if it's running off gas, especially if it is windy and blowing in the direction to the vent. Just needs adjusting and cleaning but still could have been the same for you. Depending on what the flume is made of , it could be that ie melted or moved, slipped and just reduced it going out like it did on ours the first time and just fill the caravan. Other thing I can think of is the curtains normally where they are stitched light can pass through the stitch holes and possibly create the effect. I know the blinds in the one we have do. Can't think of anything else that may cause it unless you were awaken suddenly from a deep sleep state and brain just carried on working as if a dream.