This is a reasonably frequent effect of elevated GH.
Most of the time it comes down to fluid retention, which leaves you feeling "heavy" along with tiredness.
Other times the cause is a shift in how glucose is processed, with insulin rising, producing something like "post meal fatigue".
Whichever the reason, it typically fades over the course of a few weeks while your body adjusts.
That said, should headaches, nausea, and/or vision problems appear, that may point to intracranial hypertension (IH) — an uncommon yet not unheard of and very serious side effect seen with rHGH — and you ought to halt right away, since it can lead to blindness (tbh not sure if secretagogues can cause IH, Tesa doesn’t).