system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Is it physically possible to bring a dead body back to life?

I'm not talking about hospital scenarios but say someone dies from like drowning or choking, Why can't we revive them? Also, what's the point in freezing bodies?
gpt
There are 3 main points when a person is dying:

1. They stop breathing.

2. The heart stops.

3. The brain dies.

---

Until #3 happens, they're not technically dead. 

When a person stops breathing (they're drowning or choking), if their airways are cleared they can be resuscitated (eg through CPR).

When their heart stops, ~~they can be brought back through CPR or defibrillation~~ they're clinically dead, although in some **very rare** cases, injections of adrenaline and a vasopressor combined with CPR, or the application of transcutaneous electrical pacing can bring them back to life.

When the brain dies they're ~~clinically~~ biologically dead. That said however, there have been cases where either patients are incorrectly declared brain-dead~~, or they have come back from being brain-dead~~, generally when the brain has been showing no activity but the body is on life support. This is extremely rare however. The brain works (in layman terms) by having electrical pulses jump between neurons. These neurons trigger other neurons. If the neurons all stop functioning, there isn't really anything that can get them going again, at least not in a basic pattern as before; without that pattern, you don't get a living human back; just a bunch of twitching muscles, etc. 

---

As for freezing bodies; the idea goes 2 ways:

Short-term freezing:

A lot of people die on the way to hospital, either as patients in car crashes, or as soldiers, disaster victims, etc that get badly hurt in the middle of nowhere. In many of those cases, the patient could be allowed to live by "freezing" their body (their blood is temporarily replaced and their body is cooled down, but not into an icicle), which would delay the problem for a few hours, allowing them to be transported back to a proper medical facility. This technique is the one in the news, currently awaiting human trials.

The other idea is to freeze the body for as long as desired. Currently this isn't possible as the body begins to deteriorate; cells in the body need energy and nutrients. Special fluids (the stuff that replaces the blood) can kind of do that, but that doesn't address all of the cell's requirements. 

If this and any other issues can be solved, then it is hoped that if patients have terminal diseases, or injuries that surgeons / doctors have no idea how to fix, then they can be frozen where they'll be woken up one day in the future, when the technology / medical science is good enough to solve the person's issues.

Also, some people just plain hope to be able to get frozen so that they can experience the future, or (if they're old) get their mind uploaded into a computer / have their body cured of aging.