This is unlikely to be a serious problem though, I'm afraid, the only way to be sure is to see an optometrist.
An optometrist is not an MD, but they ARE experts with the eye.
What I suspect is happening is that when you turn out the light your eyes adjust differently to the dark.
Likely, when you turn the lights back on you also have a period of time when the eyes don't see as they should. This is called an accommodation problem and is not serious.
However, there are disorders of the retina and optic nerve that can be easily seen on a simple eye exam that need to be ruled out.
The good news is that an optometrists visit will not cost too much. Somewhere between $50 and $100, and they can do a good exam on your eyes and make sure this is nothing to worry about.
Your problem, unfortunately, is not one that I can safely tell you to ignore just based on this conversation. Walmart even has Optometrists in the stores, so you may want to simply walk in and ask for an exam. I think this will be the most economical way for you to put your mind at ease.
If you have further questions about this please let me know.
Positive feedback always appreciated.