I saw a bright in my living room. Right after I used my bathroom.. but it went away so fast. I don't know what it is..

Probably a malfuntion in your light switch or carlights from the street.

There could be any number of explanations , KK gave you two to think about.
If this is the only time it has happened I would not be too concerned, it more than likely has a rational explanation.

Even if it does reoccur , the chances of a "natural" origin are much greater than supernatural.

What kind of a light did you see? Was it small or big? White or yellow? How was it shaped? Was it defined at the edges or fade out? Without more detail, I am afraid there are a number of explanations as to what it could have been.. . most of which are natural occurrences.:)

Someone opened the refrigerator door

To let you out? Or put you in?

To let you out? Or put you in?

LOL... Kit:D