The other popular thought regarding the chase is slightly more sensible. It's that one person is looking for space on the bed, so they gradually edge away during the night. The other person, perhaps needier or just more comfortable in the spoon position, follows them to the other side of the bed. Who knows, maybe they're even just a little bit cold? We really think this problem could be solved with one of those handy electric heaters.
Whatever the reason, the chase sleeping position doesn't seem to spell good news for either half of the couple. You're either playing mind games to incite a pursuit, you need more space in bed, or you're suffocating your partner with too much spooning. Maybe it's time to sit down and have a chat about what's going on in the bedroom.