The drained feeling and the headache are interesting. I have a little bit of experience using 5-MeO-DMT in a similar way to the DMTx method. It involved a mechanized self-injecting syringe that was programmed to inject very slowly at a consistent rate.
The trip itself was fascinating, but after a few hours, I was absolutely physically wrecked with a strong pressure headache and a general feeling of being unwell.
Do you know if that's common among extended-state DMT users? I wonder if the human body isn't a fan of the constant psychedelic drip.