Good job, then. Just be sure to start slow, regardless of how far or hard you ran. VFF's can cause stress fractures in the metetarsals (or whatever those little bones on the top of your feet are called) if you ramp up too quick. Do not run through pain in that area. When you start, you'll probably be really on your toes, but as distances increase, you'll switch to a midfoot strike, with you heel touching, but not at all impacting. Also, run on a treadmill to start, as it has give, and start with 1/4 mile in the vff's, then stop, throw your regular trainers on, and run a bit more. No need to be totally hampered by the conditioning of your feet and calves.
As for the caffeine...don't miss the workout. Go for an easy run, do not push it. The exercise increases blood flow and will normalize the vaso-constriction/dialation in the head. I'm sure you know this, but the headaches are caused by chronic use of caffeine, which is a vaso-constrictor. Your body wants to achieve homeostasis, so it eventually counters the constant, daily vasoconstriction with extra NO to vasodialate to normal levels. So when you stop the caffeine cold turkey, the body needs a while to taper that extra NO production off, and essentially that extra NO, without the caffeine to counter it, causes a pressure headache. In my experience, a nice easy run and a workout helps get the blood flowing, and reduce that effect. It's not harmful, just uncomfortable (or downright painful for a very few people). The lethargy just takes some time to normalize, as well. But again, getting the blood flowing makes things a whole lot better.
Go workout, bro!
