Oh man, I feel that. I started getting that weird thumb numbness while building models last year. What finally helped me was doing those wrist stretches every hour, like bending my hand back gently. I also raised my keyboard a bit so my wrists weren't bent up all the time. It took a few weeks of being really strict about it, but the tingling mostly went away. Dropping those tiny parts is the worst wake up call.
Read somewhere that numbness can be an early carpal tunnel sign. Betty144 has the right idea taking tingling seriously. If it keeps up, a short break to shake out your hands is way better than dropping parts.