Hi guys.
Well, when I am super-warmed up, even the guitar parts I can play very well (either lead guitar or rhythm guitar) gets difficult to play. My picking hand feels as if it's "flying around" uncontrollably.
I just practiced Master of Puppets rhythm parts slow, using a metronome, at around 150-160 bpm, for around 45 minutes. As a result, my hand warmed up and felt "loose" and "flexible". However, when I played the outro solo to Fade to Black a moment ago, it felt as if my picking hand was out of control. I know for sure if I was "less warmed up", for want of the correct term, I would have found it easier to play it. I did finish it well, but it was unexpectedly tougher. This always happens when my picking hand's warmed up very well.

So, will this go away with time? Do I keep practicing sections slowly?

If I played Master of Puppets downpicked with a super-warmed up picking hand and eventually came to Kirk's solo, then it seems as if I would have a hard time with it, what with a "out of control" picking hand...

Any tips or advice?
Doesn't sound like you're "super warmed up", sounds like you're just burnt out after playing MoP for 45 minutes straight... It's pretty normal, just have a bit of rest when you start feeling like that to avoid any injury.
Yeah, cool down a bit and you should be able to control yourself and your happy hands again.
I experience a similar thing. I have benign tremors in my hands and often my picking hand feels out of control. I just try to calm down and relax for 10 minutes or so and re-approach the song with a lighter more fluid movement. I notice that my picking hand/forearm gets tense when I play and often that's what results in feeling out of control. Smaller wrist based motions are easier to control for me. But everyone is different.
I'm the total opposite, it takes me about 45mins to an hour to get properly warmed up and feel that i am playing at my maximum potential. But i do find if i play too long with predominately a single technique everything tenses up and everything goes to shit.

Toodles Julz.
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