What are some ways to get past that claustrophobic feeling from a cast on the leg and foot?

I’ve been in casts before; however, this one – and it’s only been a matter of hours, is leaving me with this horrible closed in feeling. Which seems completely ridiculous, to me. I’ve never had one that was this big – foot and leg, just shy of my knee. I can’t stand to feel confined and it’s already leaving me fighting that feeling. Any hints on how to get past that feeling?