Hello and Welcome to HCM,
Thanks for writing to us.
The sudden onset of a bruise
of unknown cause should not be taken to lightly, this could be an indication of either a blood clotting problem (low platelet production or increased rate of removal of platelets from blood), a reaction to any medications you could be taking (eg. aspirin
, some pain management medication, etc.), accidental ingestion of a poisonous substance (eg. rat poison, etc.).
It is best you just visit a doctor for a blood work up, once all the results return normal, there should be absolutely nothing to worry about, and this bruise could have been caused accidentally (like scratching yourself while you were asleep, etc.).
Hope this helps you.
Wishing you good health...
Dr Saurabh Gupta.