What about if I'm singing alone but people are listening? If I were singing with someone, they'd have forwarning, OR we'd be in a key I could sing, is my theory. Does it really clash? Anyway, I think what I do is switch octaves in the same key, so I go higher for the too-low and lower for the too-high, but I think I'm in the same key, since I come back to the same place...