Hi Elo!
I used to have that fear too! If you’re really worried then you should probably tell someone like your parents and they can help you. If you want a more practical approach, i would video tape your room overnight and see if the white flash comes. If it does, you’ve got evidence. If it doesn’t, then you probably imagined it.
Don’t worry if a fire does happen. I had a fire safety presentation a few years ago, so I have some tips. If there is a fire, scream for help. Crawl out of the room and shut the door. This should secure the fire for 20 min max. Get your family outside and call 999 or 911 if you’re in America, idk where you live lol.
I hope this helped!