Ah, yes. I quite agree with you, anonymous. It can be quite depressing to sit still. Nonetheless, keep in mind that inside a metapod’s shell, your (former) caterpie is hard at work, preparing to evolve. Evolution is an exciting time for a pokémon. The energy spike alone releases a rush of endorphins, and for days afterwards, a pokémon will feel stronger, happier, and more in-tune with itself than it may ever be. I realize that sounds depressing, but imagine ten of the happiest days of your life. Then imagine experiencing everything you did on those days within a single minute. That’s what evolution feels like, and caterpie get to experience that in rapid succession. No doubt your metapod has evolved recently (compared to other evolutions, anyway), so with that process fresh in his mind, it’s likely that your caterpie is eagerly awaiting the moment when it will experience it again and take flight for the first time ever.
That having been said, if you’d like to be sure, the best way to tell if your metapod is all right both physically and mentally is by watching for any sign of movement—or, rather, by watching for the lack of movement. The stiller he is, the more he’s reinforcing himself and conserving his energy, which in turn means he’s trying his hardest to evolve into the strongest possible butterfree he can be. In other words, the stiller he is, the more likely he’s focusing all of his attention on his eagerness to evolve. If, however, he’s shaking or struggling, then it’s clear that he’s growing impatient or anxious, and it will be important to calm him down in order to get his mind back on evolving. Usually, hearing your voice will be enough to calm him, but holding him may help as well. Any sort of reassurance you can offer him that you’re still there and that you’re patiently awaiting his debut as butterfree will be enough.
Congratulations on your previous and pending evolution, anonymous!