Mitochondria are the tiny organelles that produce energy for your cells.  The  heavy metals and chemicals to which we all are exposed in the environment are toxic to your mitochondria, causing them to malfunction so they cannot produce energy.  Instead of ATP, mitochondria exposed to these toxins produce free radicals.  These are unstable molecules that cause cellular damage, inflammation, and aging.
 
What are the most common sources of heavy metal exposure?  Amalgam fillings (50% mercury), eating fish,  laptop computers,  paint in old houses,  vaccines, working as a mechanic , metal worker, technician, painter, printer, plumber, carpenter,  metal recycler, dentist or dental assistant.
 
Chronic exposure to heavy metals and chemicals (which are ubiquitous in the environment) not only leads to impairment of your body's ability to make energy, but also leads to depletion of glutathione and associated immune dysfunction  resulting in chronic viral, bacterial and fungal infections such as Lyme Disease, H.pylorii, candida, Epstein Barr and hepaptitis C.
 
Glutathione depletion also interferes with trace mineral absorption, transport and distribution and shuts down your body's ability to detoxify and excrete metal, chemical and fungal toxins so that the toxins accumulate in your body producing a wide range of adverse effects.
 
One common effect of heavy metals is impairment or inability to make T3 from T4.  Since T3 is 3-4 times more potent than T4,  this results in  a functional thyroid deficiency.  However, because TSH is more responsive  to T4 than to T3, your TSH will be in the normal range. Your doctor most likely will tell you that since your TSH is normal, you don't need treatment, even though you may feel terrible.  This phenomenon can also be caused by selenium deficiency since selenium is a cofactor for the deiodinase enzyme that converts T4 to T3.
 
Another  common effect is the overproduction of reverse T3, a molecule which is the mirror image of T3 (your body's most potent thyroid hormone).  The high level of reverse T3 blocks the action of the T3 so that your metabolism is slowed and your body temperature is below normal. You will then experience the various manifestations of thyroid hypofunction, such as weight gain, fatigue and feeling cold, except that your thyroid tests again will look normal.
 
The presence of heavy metals in your body causes your body to act like an antenna, enhancing the strength of electromagnetic fields in your environment and producing the disturbing manifestations of electromagnetic sensitivity. This can cause irritation and brain fog  in people speaking on cordless phones, working in offices or laboratories with multiple electronic devices, laptops or various wireless devices, or working or living close to cell phone towers and antennae.  The problem is becoming much more widespread, especially since the intensity of EM fields in the environment has increased over a million fold in the past 10 years.