Quantum Immortality.
So, here's the deal. People die. You know that already. You on the other hand, don't. Well actually, you do, but to you, you don't. You might recognize this as a basic quantum concept: Schrodinger's Cat. Only the cat can truly know whether it's alive or dead, and for outside observers to know for sure they must remove the box.
There are far too many stories with consistent hallmarks/tropes (i.e. the time slow down/"jump back") for this to be a co-ordinated LARP. r/GlitchInTheMatrix (can't remember if it's the one with underscores or not) has hundreds of stories which follow the same basic pattern. Below is a four-stage guide demonstrating how Quantum Immortality works and how to react accordingly.
Stage 1: Death
During the first stage your body and emotions will undergo the worst trauma they have endured in their life. You will feel dead, and you will know you are dead even though you shouldn't be able to. You shouldn't perceive any injuries since your central nervous system has undergone what many in computing would consider a stack overflow, that is to say pain is being sent to it, but it isn't being received.
Stage 2: Object Distortion
Whatever happened to you, you will not perceive it as you should. If you're involved in a traffic accident, you won't feel the vehicle or wall crush you to death. Instead you'll just go through it, as it seems your body has already released its grip on life, and is only relaying you visual stimuli that would make sense. Again, like computing, imagine playing an online game with extremely high ping. Stuff will move around you free of collision. Some people have reported OOBEs (i.e. seeing their dead body in front of them).
Stage 3: Time Distortion
Once dead, time cannot physically progress since it can no longer be perceived by your carcass. However, time is infinite, and it absolutely must continue, so a "compromise" is reached. A few seconds after your apparent death, you will sense time changing speed, with many reporting a slow down before a stop, and either a rewind or a skip to a couple of minutes prior, and you get a "second attempt" at whatever it was caused your doom. This can happen more than once; a story on reddit had an OP who continually got shot by a mugger until he eventually overpowered him, whereas another saw their own coworker fall from a ladder and crack their head open multiple times until they were able to do something which stopped it (for some reason, that particular instance affected the main witness, which is the only instance of QI-by-proxy I've ever seen).
Stage 4: Life
With the QI Event drawing to its conclusion, there is not much else for you to do but suck it up and continue with your life. Yes, you are dead in the world you once knew, but crucially you are alive in many others, including the one you're in now. This also proves that alternate universes/timelines are a thing, and you've probably gone through several unknowingly.
