Yeah, that's a blood blister. they form as big swollen lumps when the trauma is heavy at a single location. The flat and spotty one you describe would be the result of multiple minor traumas. Stubbing your toe like you said can easily cause it. I remember when I got a blodo blister. a huge scrape on the bath tub faucet along my foot (Don't ask how, I never figured out how I managed to pull that off.) and it created this terrifying huge purple/black sac across the entire side. That's the sort of injury that leads to the big inflated ones.