Hey _bob. Great question. Trust Level 3, where you were at, can be lost if you don't meet all of the Trust Level 3 requirements over the last 100 days. It's outlined above in the explanation about Regular (3).
Also, the promotion and demotion is done automatically by the system, out of the hands of the moderators, as it is time based and calculated over the last 100 days.
Let me know if you have any other questions.