What Side Effects Can I Get From Thallium?

What side effects can I get from thallium? It has been told that I can lose my hair. The test , stress test was advised to find out why I had a racing heart. All tests so far, blood work , electrocardiogram, echo cardiogram were perfect. I am 83 and healthy in all the vital signs. I have had side effects from many meds that were given me for other problems proving I have allergic reactions.