For some reason, my endurance has seemed to plummet over the last couple of weeks, and I don't know how. I've recently (past few days) tried to minimize the mouthpiece pressure I use, but otherwise, I've been playing pretty much the same way I always have. I mostly play straight through songs and skip fundamentals, although that's what I've been doing for the last year or so and my endurance hasn't taken a hit until now (I'm trying to give fundamentals more priority now). I also typically do all my practicing in one long session.
I'm not feeling the fatigue in the center of my lips, which is good, but I'm feeling it heavily in the corners of my mouth and especially the facial muscles like in the cheek area. It's at the point that my face feels worn out consistently day after day, even after taking a day off of playing. Even after doing just a 10 minute warm-up of flow studies I already feel like I don't have a strong high C in me anymore.
Do I just really need to stop playing for several days, use ice, play long tones, or what?
Any advice would be appreciated.