If you speak on any kind of regular basis, you're going to have times you simply don't want to go up in front of anyone and talk, much less connect, entertain, and inspire to action.
Sizzle or Soothe. While many coaches will tell you pop is the last thing you want to drink before a speech, drastic times call for drastic measures. If you need a pick me up, go for it. Grab a 4-hour energy or a Mountain Dew. Don't want the sugar? Get some strong coffee. If it's stress you're dealing with, drink some soothing tea, or get some comfort food. Sometimes a candy bar, while not incredibly healthy, can change your mood just in time.
Move. Not away - you still have to speak. Get your body moving. Stretch. Do some push-ups against the wall, or walk briskly down the hallway. You'll get your blood flowing, take out your tension on the physical exertion, and gain some focus time.
Escape. Even if you can only grab 5 minutes in a janitor's closet, get away from everyone and everything. Refocus on the purpose your speech, and the benefit it has to the audience.
Visualize. Imagine yourself in a position of strength and energy for the duration of your presentation, culminating in a successful result for your audience.
Straighten and Shake. A shift in posture - back straight, shoulders back, followed by a calm shaking out of your arms, legs, and neck can do a lot towards re-setting your physical state and easing your mental tension at the same time.
Smile. Amazing what a smile, even a forced smile, can do for your attitude. Even an exaggerated smile in the bathroom mirror (try your best Jack Nicholson impression) can uplift your mood by way of absurdity.
The above are great for weariness and bad-attitude days. But what if you're facing real physical challenges?
Medicate. Time your medications to take effect just prior to your speech, so you get optimum results. Don't take too much, or medication that will leave you tired or out-of-touch. Don't mix your medications with alcohol! Plan ahead for headaches, backaches, etc., or you'll find yourself paying 500% markups in the hotel gift shops...
Yield. In my case, I've had days where walking is very difficult, even impossible, whether due to my back or my leg. It's OK to give in to physical weakness and ask for a stool or chair on stage. If this happens regularly, ask for a ramp to be set up to the stage, and have a wheelchair handy. Better the audience knows you're in pain up front - that way they get past it quickly and stay with your presentation content - than sit wondering why you're grimacing for 45 minutes.
Whether you are in the mood to Speak & Deliver or not - your audience deserves your best. Take care of yourself so you can focus on them!