My wife and I discussed this at length. 4 years ago, she died twice in 3 months, needing full resuscitation both times. Both were lengthy rescues (one resuscitation was off-and-on for nearly 40 minutes).
I asked her later when she had recovered if she remembered anything at all during the times she was clinically dead. She remembered nothing. Blackness. No light. No relatives and former pets waiting for her. Just…black. Thankfully, also no pain.
She finally passed 18 months ago, and I hope she felt no pain or worry the final time.