The most common causes for bruise
in a person is injury
,as you had it.
But there can be various other causes of bruises like consumption of anti inflammatory drugs,aspirin
,CLOPIDEGROL,heavy consumption of garlic,use of natural products like ginkgo biloba
Just wit and watch.If you find that ou are getting multiple bruises and occuring repeatedly,then you may consult a doctor to get the necessary blood tests done to find the cause and manage the problem.