First angry part= pain, suffering thats going in his life. You have the drug "tempting" him as relief saying "Trust in me, trust in me", etc.
The middle part=one is THROWN into temporary numbness by the drug. Even though the music suggests a nice, pretty tone with the flutes and and stuff...there is an underlying darkness behind it, based on the background sound effects of hospital sounds, etc.
Last part= but as all relief from drugs are, its only temporary and not fufilling. So just as quickly as ur thrown into paradise, ur kicked out of it, back into chaos--abruptly, suddenly, and disoriented. So now ur back into the mess u were in before, except its even worse.
Thats my take.