When I am really stressed about something I will get a twitch sometimes. It can last for days and only started happening in the last few years. It has happened twice that I recall. Both times it just felt like a muscle contracting involuntarily.
The first time it was the muscle around my left eye, it would contract and move my eyebrow slightly, I found it extremely annoying. The second time it was a muscle in the left side of my neck, it contracted in rhythm with my pulse, and I actually went to the doctor thinking it was something else, like I was at risk for a stroke or something.
After a series of tests, echoes/ekgs and all that, the doctor said I was fine. That was when I realized it was a twitch, because it had gone away after several days once I was less stressed again.
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"Knowledge speaks, but wisdom listens."
- Jimi Hendrix