I'm not certain on the reason it happens, but it can be lethal by stopping the heart from beating and, the lungs from contracting and expanding causing death by suffocation or cardiac arrest, also putting the body into shock.
Answer: In most chemical reactions, bonds are both broken and made. Energy is absorbed when bonds are broken, and released when bonds are made. The sum total of the released (negative) energy and absorbed (positive) energy determines whether the overall reaction is exothermic or endothermic.
Hope this helps!
Increasing is what I think
