For the first 5 or 6 days of my bout with pneumonia, why did i have such an excruciatingly painful headache? (i could barely talk or move!)

HA with pneumonia: One type of pneumonia caused by mycoplasma is commonly associated with headache. Dehydration may also play a role.

AllSystemsConnected: First, any infection in one place can have side effects in another. Think of the flu, aches, cough, sore throat headache fever. So in your case: something like fever, loss of appetite, congestion and frequent coughing either causing a headache or making one worse. And with infections like pneumonia there can be inflammation that develops in the brain. Could get serious but in your case it didn't.