In my experience, neck cramps are not usually a symptom of something more serious. They are usually short lasting and will resolve on their own. Any trouble coming from his heart should be more of a pain than a cramp, and is usually associated with shortness of breath, chest pain, arm pain or jaw pain. His thyroid is also unlikely to give him a neck cramp.
It is possible that his cramps are being caused by an electrolyte imbalance from medication. You should have his doctor check his bloodwork.
Although he works with some chemical, I strongly doubt this is the cause of his neck cramps.
In the meantime, I would have him put a warm compress (heating pad ) on the neck and try some gentle stretching. If it continues or gets worse, please bring him to a doctor to get checked out.
Thanks for being a concerned wife - he is a lucky man!
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