Thanks for writing to us
Normally, bruises will fade away in 10 to 14 days without any treatment.
A bruise is a wound caused by blunt trauma
resulting in bleeding from minor blood vessels under skin and soft tissues. The discolouration of the bruise is due to blood pigments deposited in skin. The swelling associated is due to the accumulation of blood or inflammatory fluid in the wound.
According to your description you seem to have a bruise due to ruptured blood vessel causing the sudden increased swelling by accumulation of blood.
If the bleeding is minor then there will be not much increase in the swelling, however the pain and discolouration might persist for couple of weeks.
I do hope that you have found something helpful and I will be glad to answer any further query.