The blue pill is not made for every1, and the chemical reactions may be due to food intake, other drugs such as prescription and alcohol, chemical imbalance, and the list continues. I am sure you have read the warning signs to avoid certain things while taking the blue pills.

Anyways, I haven't had any experience with this pill, so I cannot comment on this. If you do experience these symptoms regularly, you may want to consult with your doctor about it. Its a prescribe prescription, so you may want to follow up with the same doctor that prescribe you the blue pill and inform him of your situation.

Just my guess: since most gentlemen who take these pills are in their 40's and up, the stamina, energy, and work that is produce during the intoxication period may cause you to burn out after the effects. Meaning, you exert more work into the session than what you regularly do without the pill, and your body may not be use to it--hence the burn out. Again, just my guess.

Specifically how do you feel?  
I do have the headache, usually more after the session & sometimes worse than others. Advil works quickly and quite well. I don't take the Advil 'til after the session though as I don't want to have any effects on the Viagra. Sometimes my eyes have heightened sensitivity to light. Sunglasses work for that.

I have not experienced any other "hangovers" from the blue pill. I feel great after a session.
I have no other prescription medications.

....I got a lower back pain that I completely dismissed as having anything to do with its use.

My doctor is the one who let me know of this particular side effect that some will experience.

1/3 of a pill + a shot of Afrin works for me.