Hmm, everyone else's issues with numbness in the hands seem to actually reside in the hands. For the last half-century or so of my riding career, my hands will go numb when I allow my neck to drop into my shoulders as I ride. If I hold my head up (the good posture my mom encouraged!) the numbness goes away.
Same here. Old C2 neck injury from 2001 car wreck, and re-injury last year, make my neck and shoulder position more critical for comfort on longer days in the saddle. I'm constantly correcting my tendency to hunch up my shoulders.
And I'm hyper-sensitive to stem/handlebar position. Which reminds me, I need to either lower or raise the stem on my hybrid. I put on a longer road bike stem a couple of months ago and while the reach is better with long swept albatross bars, the height feels like it's often in the no-go range. A slight adjustment to my hand position on the bar, higher or lower, alleviates the crunchy neck sensation.
I've been back in PT for a month and it's gradually improving my posture and comfort.