AS far as I know, the deliriant effects of nutmeg come primarily from myristicin and elemicin. Myristicin is both a weak MAOI (monoamine oxidase inhibitor, which causes it to inhibit breakdown of several neurotransmitters, including serotonin, norepinephrine, and dopamine), and a decently strong anticholinergic agent; elemicin appears to just be an anticholinergic. As far as I can tell, anticholinergic drugs in large doses cause a whole bunch of physical and psychological effects, including delirium and extremely realistic-seeming hallucinations. They also cause a wide variety of unpleasant physical symptoms at those doses, which is why tripping on nutmeg is generally as unpleasant and foolhardy as tripping on datura. It's not really an experience you want to seek out unless you're looking for something very particular.