Brief Answer:
Needs neurological examination and work up

Detailed Answer:
Hi! Welcome to Healthcaremagic. Thanks for sharing your concerns with us. We will try to help you in best way possible. First of all it's sad to know what you had been going through lately.

Based on the history you have shared, it's less likely to be due to TMJ. possibilities may range from BPPV, Migraine and TTH however detailed neurological examination is a must to differentiate between these or include other neurological causes like cerebellar issues or any vascular or space occupying lesion.

Intraocular pressure to rule out glaucoma and visual acuity and visual field to rule out any compression on visual pathway inside central nervous system needs to be done.

After the examination it would be easier to chose between brain imaging like CT or MRI brain, fundoscopy for signs of raised intracranial pressure, metabolic profile including electrolytes levels, B12 and folic acid levels as well as endocrine work up like thyroid profile and sugar levels etc

Heart test which you mentioned, if EKG which was normal, it's better to get a 24 hour holter monitoring to rule out any abnormal heart beats causing abnormal blood flow to brain etc but the heart seems less likely.

Treatment would depend on the cause however OTC analgesics like acetaminophen or Ibuprofen can be helpful for symptomatic relief initially. Wishing you a speedy recovery. Hope this has answered your query. Otherwise feel free to ask. Regards

---