When i smoke crack, i get a scary strangling sensation. what could this be?

Cocaine delivered in the form of crack acts very rapidly and is then just as quickly metabolized so it puts your body and brain through some extreme changes very rapidly. You don't say at what part of this cycle you experience a strangulation sensation but if happens right after you take it, it could well be due to cardiac arrhythmia which can be dangerous, even fatal. You need to stop using crack

That is likely a spasm on the coronaries or the vessels irrigating the heart muscle. That is as close as it gets to a heart attack. Time to make changes in your lifestyle.