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This may be basically bruise caused by blunt force trauma to the body that crushes underlying tissue and damages blood vessels without breaking the skin. So nothing to worry about primarily.
Next Steps
Just to make sure it's a no-worry, look if there's any other such marks anywhere over body, inside mouth, under tongue. No means all is well.
To make you utter sure about this, just run blood tests: CBC, PT/INR
Health Tips
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