Yes, you are shut down.
Most individuals produce approx 10mcg of Free T3 per day - taking 25mcg of T3 that attenuates within the body in 4 hours WILL shut you down. You will recover in a few weeks, but your thyroid will likely not be at the level it once was, and you can verify this through bloodwork. Your T4 will likely be high, T3 low, and TSH high.
This has been my experience. My thyroid is not working as well (verified through blood tests) since taking T3, and I do regret it. I've recovered but its not optimal-
Optimal and youthful range for TSH is between 1 and 2. Upon testing it was higher, and I don't convert T4 to T3 properly anymore....
Edit: I was only taking 20-40mcg of Tertroxin T3 per day in conjunction with ECA.