If you get elevated mercury levels, how do you feel?

Varies. Mercury can be elemental, inorganic, or organic and symptoms change depending on type and if exposure was ingestion or inhalation. Inhaling elemental mercury (old thermometer, fluorescent lights) can cause difficulty breathing, vomiting, bleeding gums. Bloody diarrhea/vomiting, kidney and brain damage can occur from swallowing inorganic mercury (batteries, disinfectants). Organic mercury ...
Multiple. Memory loss, mood swing, skin rash, muscle weakness, mental disturbance, lack of coordination of movements eg writing, impairment of speech, hearing and walking and loss/ impairment of peripheral vision , pins and needles, feeling, numbness around the mouth , hands and feet.
Brain fog. The list for mercury toxicity is very long. If you google it you will see.