I think one of the best things about having a big part in a play is the high that you get after a particularly successful performance. I always feel so "on" in that situation - extra confident and witty. For example, after one rehearsal of Cash on Delivery we were trying on the costumes for the first time. One of the other characters was wearing an absolutely hideous dress and I made the old joke "It's very becoming. Though I'm not sure quite what it's becoming..." which seemed quite out of character for me. Maybe I was just starting to feel comfortable in the presence of my fellow cast members or maybe it was a natural high caused by the adrenaline of the situation. Almost like being drunk, but with no hangover in the morning.