Every night when my bedroom is dark a green glowing circle on the floor appears What does this mean?

there is no mistake about it,

it was a ghost!! Maybe you spilled something on the floor that has turned out to be luminous. Try covering the area with something lightproof for a couple of days, then remove the cover after turning the light off and see if it still glows. If it does, you may indeed have a ghost (but probably not).