i lack any understanding in science. so a little help please.

ive been reading debates as to wether heroin overdose (or a mixture with other drugs, speedball) is a painfull way to go.

most say that it is painless, and they fall asleep and die.

but ive read that heroin overdose causes 'respiration depression' and the person basically can't breathe as its brain is not sending the required messages to the lungs.

so how is it painless,? isn't it just like suffocating to death?

..my friend passed away 2 years ago becuase of this. i just want to understand this.