I had to look up HGH (Human Growth Hormone) therapy
Human growth hormone (HGH): Does it slow aging? - Mayo Clinic)
I hope you've discussed the fasting plan with the prescriber of the HGH therapy.
Are you struggling just with low energy? Certain breathing techniques can be stimulating, as well as splashing ice cold water on your face and arms.
Does the therapy increase your appetite? Perhaps drinking water or seltzer with lemon might help.
The "Hay" in the Hay diet (Dr. William Howard Hay) advocated fasting in "Health Via Food", but he'd put his patients on weeks-long fasts, and he'd remark that energy resumed at about day 3 of the fast. He also had different degrees of fasts. For example, he claimed that a diet of fresh fruit or vegetable juice was a fast.