In the world of functional neurology, we have a number of ways to test the state of the nervous system. But the first thing I do with every client is perform a couple high-level checks looking for either "global hypertonicity" or "switching."
Let me preface by saying that the nervous system follows very firm rules. A useful analogy is to think of traffic: green means go, red means stop, a right blinker means a right turn, etc. When everyone abides by these rules, the "output" is normal and functional. That is, everyone gets where they're going in one piece. (Just ignore the variables of people not paying attention, bad weather, etc. for the purpose of this analogy.) If suddenly someone decides red means go, then chaos ensues.
The nervous system behaves in the same fashion. Specific stimuli should always elicit a specific response, even when the stimulus is very low level. e.g. if you hold your arm out in front of you and I press down, the deltoid should be strong enough to keep your arm in place against a reasonable force. But if I touch you even lightly on the top of the hand with something sharp, you *should* lose the ability to hold the arm up against force. This is just a very low level withdrawal response, differing from pulling your hand away from a hot stove, or pulling away from someone tickling you, only in the strength of the stimulus. Again, this is a normal, healthy response.
Someone who is globally hypertonic (literally, "too much tone") does not respond to any low level stimulus. A light poke on the hand, a "spindle cell compression," cartilage reflex (how a bull ring works)... none of these actually create the response they should. It's analogous to being plugged into a socket. There is a source of electrical noise in the system loud enough to seize up the works. Now, if you actually touch a hot stove, that is certainly enough stimulus for the brain to "hear it" over the source of electrical noise, and you will pull your hand away. The problem is that *most* of our need for proper response to stimulus is not an emergency. i.e. the stimulus is much lower. And the brain cannot hear or respond appropriately.
Someone who is switched is in the highest state of neurological disorganization. Instead of being non-responsive, their brain responds, but chaotically and incorrectly. These people, if they have been in this state long enough (years), will often present as jittery, uncomfortable in their own skin, mentally slow, ADD, brain-foggy, easily startled, etc. All of those symptoms are the result of a brain that can't tell green from red, left from right, start from stop, etc. The brain is basically guessing how best to respond.
With my experience, I can tell if I am personally in one of these states almost instantly. Most people cannot. Like smoking cigarettes or living on junk food, you probably aren't going to notice the symptoms in the short term. But you'd damn well better believe you will notice them in the long term.
Both of the problem states I just described come from having too much electrical noise in the system. The brain depends on accurate, consistent, reliable information (in the form of electrical input) in order to keep you functioning properly. When that input becomes aberrant, then the output becomes aberrant. Over time, this leads to pain, weakness, poor organ/gland function, and any variety of symptoms.
The problem with strapping a high-powered electrical device directly to your body is that the device is a source of electrical information. It can't read your nervous system without interacting with it. And if it's interacting with it, it isn't just receiving information, it is sending it. And the information is garbage. Your brain isn't capable of saying, "Oh, that information is coming from a foreign device, just ignore it." Your brain is responding to every byte of information it is receiving 24 hours a day. It has no choice but to attempt to process and respond to the electrical information (either direct, or via EMF) its receiving. Again, if the information is gibberish, the responses will be gibberish.
I have never, ever, seen someone who can wear an iWatch and still exhibit normal neurological responses to stimulus. They are always either globally hypertonic, globally weak, or switched. As soon as the watch is removed, they return to normal. Sometimes, I can just cover the sensors on the back of the watch with electrical tape, and the watch no longer causes this effect. Other times, it's still a problem, indicating the issue is probably not direct input from the sensors, but rather EMF.
This is not negotiable. I have hundreds of colleagues doing this work around the country, and they all find the same thing. Whether you experience symptoms and how quickly depends on what else is "wrong" in the system (i.e. how much noise is already present by default), and how much processing power your brain has. (Processing power has no correlation with intelligence.) A person with a faster processor and more RAM (to use a computer analogy) can tolerate more noise in the system without experiencing symptoms. And some people can smoke cigarettes for 50 years and not die of lung cancer. That doesn't mean smoking isn't bad for your health.