People with high platelet levels often don't have signs or symptoms. When symptoms occur, they're often related to blood clots. Examples include: 
Headache.
Confusion or changes in speech.
Chest pain.
Shortness of breath and nausea.
Weakness.
Burning pain in the hands or feet.
 Less commonly, very high platelet levels may cause bleeding. This can cause: 
Nosebleeds.
Bruising.
Bleeding from your mouth or gums.
Bloody stool.
