So, when Stalker suddenly collapsed last month during an exercise class with her 12-year-old daughter looking on, no one would have guessed the 41-year-old was the victim of a life-threatening rupture in one of the blood vessels in her brain.

Scarcely a month later, Stalker is almost fully recovered following an emergency operation at Rhode Island Hospital in Providence, and looking forward to resuming her busy routine.

She credits employees and fellow members at Olympic Fitness in North Attleborough, paramedics, and doctors for their prompt response in her case. ‘‘I’m feeling like a pretty lucky chick,’’ said Stalker, who suffered the ruptured brain aneurysm Jan. 13.

An aneurysm is a weak portion of a blood vessel that balloons outward from pressure. In some cases, the pressure becomes too much and the aneurysm bursts, causing blood to leak out into the brain.

Only about 50 percent of rupture patients survive, said Christine Buckley of the Brain Aneurysm Foundation, which spreads aneurysm awareness. Of those who live, many retain debilitating after-effects because of damage left behind in the brain.