Why would a heavy meal, or chest congestion, affect heart rate? mine can palpitate or slow right down in both instances even when resting in bed.

Metabolic demands: A large meal requires 'resources' to be directed to the stomach -i.e. blood! Blood carries vital oxygen and nutrients to tissues (such as the heart) - so a huge meal may infact affect blood flow in some ways. If a narrowing of an artery exists somewhere (such as in coronary artery disease), this change-up can have end organ consequences. With chest congestion it's different, but you should see MD