Thrombocytopenia is a condition in which you have a low blood platelet count, Platelets stop bleeding by clumping and forming plugs in blood vessel injuries, which means once a person in such condition bleeds, it's almost impossible to stop the bleeding if it was very low. average is between 60k-120k, if lower than 30k it means dangerous, under 5k is really really bad and in need for treatment asap.

Got the covid-19 vaccine

An illness/condition in which you have a low blood platelet count, once a person with that condition, starting to bleed it's almost impossible to stop specially if the platelet count reached 1k

average amount of platlets in the blood is usually around 50k-70k