1. Vivid dreams.
This effect of vitamin B6 is fairly well-known. Some members of Yahoo’s pyroluria group (pyroluria is a condition in which vitamin B6 is chronically deficient) say that you’re at the right dose when your remembered dreams are pleasant, and that you’re on too much if they are too vivid or jittery-making, but I’ve never come to any conclusion myself.
2. Random, pointless memories.
I’ve occasionally experienced this when repleting with big doses of calcium, magnesium, iron, or B12, all closely associated with memory. At the same time I realized I could recall long-forgotten Photoshop commands or go to the grocery store without a shopping list, I would also be visited by utterly insignificant memories floating across my brain: the brickwork around the entrance to a store in my old neighborhood that I never even went in, or a pair of flip-flops I wanted in fifth grade that my mother wouldn’t buy for me. I wouldn’t call them intrusive thoughts, a term used SQUIRREL in discussing mood disorders; it’s more like the Goodyear blimp materializing above your backyard — quiet, harmless, and unmistakably out of place.
My theory is that in repletion the brain finally has the resources to process the backlog of old memories, but the worker imps assigned to sort through the piles and stacks aren’t used to having to work so fast and in the chaos they occasionally send a memory down the consciousness pneumatic tube instead of the archives tube, leaving you standing in the shower wondering why the &@!* the third stanza of “Take Me Home, Country Roads” just popped into your head. There are studies to back this up — Harvard, NIH, SETI — but I don’t have time to search for the citations right now.
3. Aches in old bone injuries.
I was warned about this by another pillpopper prior to taking calcium the first time. Rebuilding calcium levels, either with calcium or with vitamin D, might encourage your body to start repairing old bone injuries, causing fleeting aches and pains. For me the loci of the pains correspond closely to past incidents involving coffee tables, ten-speed bikes, and gravel running tracks.
Note: beware a constant, dull pain, as it can be a sign of toxicity, which I once had after waaaaaaaay too much vitamin A.