A flawed episode, to be sure, with perhaps more than its share of non-sequiturs and contrived situations, but at the same time, one with lots and lots of suspense. And a few interesting revelations.
The defibrillator may have been damaged in the process, but it did work. And as to Talinn conveniently having the equipment on hand to climb into Picard's head, well, she's an agent of Aegis. A

supervisor, in fact. All that's missing (so far, at least) is the cat. She's prepared for
everything; it's part of the job description.
And remember, Renée's depression and anxiety were artificially intensified by Q's influence. And quite right, not all astronauts are John Glenn ("Mr. Clean, the Marine," happily married, to the day he died, to a church organist with a severe stutter).