hi theere, it is indeed a bruise
and it must have occured when you hurt yourself while walking or accidently hit the chair or bed. Check if you have any more such bruise any where else or in the recent past if such episodes have occured. If yes then you may get your bleeding time
and clotting time done. If there is any derangement then you will need to visit your health care provider and get further investigated. If not ,do not worry and the bruise will subside on its own in a weeks time. Take care.