What caused his amnesia? Did those pills have any role?
*Spoiler alert*
I don't think the movie ever explained the exact cause of "Mr. Buddwing's" acute amnesia. I was thinking that after he discovered Grace had attempted suicide, he freaked out and took some of those pills we saw him take from his pocket in the opening sequence (the exact type of which was never disclosed). Maybe he OD'd on some sort of strong barbiturate-like substance that knocked him out for awhile, and also caused amnesia?
‘Scuse me, while I kiss the sky — Jimi Hendrix