You dont specify how long you've been on the ephedrine, but I can tell you from personal experience that after being on (at least one ECA a day) for over a year, going even one day without caused a SERIOUS crash. To the point of zero energy. Bloodwork from my doctor indicated low enough thyroid levels to justify prescribing me a T4 med and recommending I hop off the ECA.
Its been around two and a half months since that diagnosis and my energy has returned to normal.. honestly, it was likely more due to the long term ephedrine use than it was the thyroid meds.
My advice, cycle ECA 4-weeks on, 2-weeks off. Any longer term use and you are asking for messed up energy levels.