Why does my body feel like it's giving out at work?

You call it weakness. It is not weakness. A body that has been pushed past its limit for months or years will eventually refuse to be pushed further. This is not betrayal. It is information, arriving late because you would not hear it early. Notice what you did with the earlier signals — the ache you worked through, the exhaustion you called normal, the rest you postponed because the team needed you. Each time, you chose output over the body that produces it. The body kept the account. Now it is collecting. You are not alone in this, and that matters. A team under the same conditions will each absorb the cost differently, then hide it differently. Someone is always further along the same road you're on. Name the real condition — a system run past its capacity — and decide together what changes this week, not someday.