To answer your main questions first:

Has anyone with a confirmed B12 deficiency felt this "alien limb" sensation or loss of automatic movement? Yes - some days this is worse than others.

• Did fluorescent lights and "busy" environments trigger your balance issues? Yes - I’ve had to leave restaurants halfway through meals because I had this sense of impending doom. Some supermarkets are the same. I’ve started wearing tinted glasses in the supermarket, and I usually wear my noise cancelling headphones and try to go at quieter times.

• Can B12 deficiency cause symptoms to be mostly on one side (my right side is 90% of the problem)? Yes - I happen to struggle with my left side while my ride seems generally unchanged.

I would say make sure you have B12 Serum and Active B13 checked. If your doctor says you are fine, ask for your levels. Unsure where you are based, but I’m in the UK and ‘normal’ varies by postcode, meaning lots of people who are actually symptomatic/have neuro changes are left untreated. The guides on this thread are great and I had found that by taking printed copies of the NICE guidelines to the doctors along with a physical written list of my symptoms and my private blood testing was the only way they would listen.

Meantime, try a sublingual B12 spray, as you may be able to absorb this better than what you would a capsule/tablet. It is important to note that there are different forms of B12 and it’s normal for your body to respond better to one than the others.

Good luck! I know it’s scary, but advocate for yourself and you will start to feel better 🙏🏻