Is the pain from testicular torsion really bad?

Very painful: You won't mistake this pain, you will need emergent surgery otherwise, you my loose that testicle. The surgeon will detort (untwist) the testicle and stabilize it. Make no mistake, you won't confuse the pain this causes.

Yes, usually...: Yes, torsion-related testicular pain is really bad, especially the commonly described one-way full-blown case.