(n.) an effort or exertion beyond your actual strength, which leaves you utterly exhausted
It might be that you have a tight deadline coming up. Perhaps a project you have been working on for months just needed one last push to complete it. Or maybe you just absolutely had to catch that train—and, as it happens, running through that station in those uncomfortable work shoes really was not a good idea. That impressive but exhausting or effort, which leaves you utterly crushed on the other side of it, is a birst.
A regional play on burst (which likewise originally meant merely ‘damage’ or ‘injury’ before its meaning changed in the 1600s), a birst is “an exertion beyond one’s strength,” according to the English Dialect Dictionary, and in particular one that has “evil consequences.”
Quite how evil those consequences are depends both on the context and the effort entailed, we can presume, but when you have overworked or overdone things and are left utterly drained as a result, you can safely say that last great effort was a birst.