What Causes Sudden Bruising All Over The Legs?

hello, i am a 20 year old female. This weekend i had a practice riding a bike as i hadnt done so for years, but was shocked to wake up this morning with my legs smothered in lots of bruises!! and what scared me the most was i didnt fall off once or even hit my legs anywhere, they are just copletely covered!
I have always bruised very easily but this has really panicked me!

Please help!!!