Please READ this!
The scene with Harry in the hospital bed acting "stupid", has nothing to do with him beeing on morphine. I tried to do an in depth analyze of questions in the review-thread, and that thing about Harry acting so "goofey" as you say was one of those I tried to explain.
See, my theory is this!
Did Harry ever really enjoy life!??? I mean, how could he, with a father whom he knew wasn't proud of him for who he was! This was already shown in the very first scene between Harry and Norman, in Spidey 1. Harry ALWAYS felt the pressure of measuring up to his fathers expectations of the perfect son. A title he NEVER achieved from his fathers point of view! And it IS true, what Harry tells Peter in Spidey 2; Peter stole his fathers love!
Harry had a heart full of hate and vengence within him. Something he carried around in all of Spidey 2. He was going crazy having the image of his fathers ghost tormenting him from within; constantly in his face, telling him to kill Peter!
As I said, Harry never enjoyed life (this is pretty obvious) way back from Spidey 1. If that wasn't enough, he goes crazy feeling the need to kill his best friend; his ONLY chance of earning his fathers full accept (which is something he's searched for his whole life)! "You will always be weak until you take control". That's his father telling him what to do!
Now to the point! When Harry gets amnesia in spidey 3, he wakes up feeling like a million bucks! And it's not because of no damn morhpine. All the HATE, GUILT, VENGENCE, and PRESSURE he felt all his damn life is suddently gone! Gone with the wind! He doesn't remember non of that! He remembers his father, yes. "I just wish I could remember more about him...who he was" Harry says. Peter replies "He loved you, that's the important thing". So why, even though Harry can't remember more than that, should he feel sad?? He doesn't remember nothing about pressure or anything else, as I've said! Just that his father loved him (or so he's let to believe). "A bumb on the head, and I'm as free as a bird", remember Harry says that to MJ!? Those lines have meaning, you just gotta read between the lines! So please do so!!!
So, in closing, the way I see it, it's fully understandable that he acts like a silly little kid, who just won the chance to start over; beeing what he wanna be. And in Harry's case, I'd take amnesia as a gift too, considering his life before that.
This isn't even a theory of mine any more. It seems pretty obvious that this is the way to understand his behavior in the film, even though it isn't too obvious explained in the movie.
