Why are we evolved to do this?
"Oh sh*t, that was traumatic. I'll never eat these gorgeous little berries if they caused that".
On the other hand... "maybe if I take just a bit less, I won't almost die but just have a great trip". Hence, psychedelics.
https://science.howstuffworks.com/life/evolution/stoned-ape-...
It is just a side effect of some other mechanism that likely has a use during our lifetime.
Until we can run control variables over billions of years…
If your heart stops, oxygen is going down, it could just mean that your brain regularitory features stop working as designed and it's firering more random.
More random / lsd / drugs can give you weird effects. Optical, sensorical etc. illusions.