Well, I'm most certainly no medic, so my opinion is thoroughly uneducated in this regard, and I freely admit this and thus am providing nothing but my own opinion on the matter--in other words, I come to no conclusions, and state merely a hypothesis. My hypothesis is that whatever drug Michael was under (if any, although I have to admit it seems likely) was a benzodiazepine. These are known for their use in treating anxiety/panic disorder and (less effectively) for the treatment of insomnia. Therefore, it could be possible that Michael was given said type of drug to deal with either (or both?) problem.
Having never taken said medication, (and, again, being no medic and pretending no medical expertise whatsoever), I cannot vouch whether or not his reaction to this medication was typical or atypical of those who are administered similar doses (in itself difficult to conceive, as we do not know how much he was given--or when-- at the time this recording took place).
However, diprivan is used as an anesthesia agent because of its rapid effect--meaning Michael would not have time to utter all he said while under its influence, assuming he reacted to it in typical fashion.
The fragmented mode of thinking (going from talking about the concert tour to talking about building a children's hospital) without any linguistic connectors (the thoughts were coherent, but the verbal connection was incomplete), the deepened voice (I am aware his actual voice was deeper than the one he used in public, but in my humble opinion, this seems deeper than the voice featured on 2000 watts--again, I claim no expertise whatsoever!), and especially the significantly slurred speech (observations of sedative effects taking place) are all indicators of being under the influence of some type of chemical substance.
However, I commit myself to nothing, not knowing with full clarity the facts of the event. Therefore, the above stated is all educated speculation.