Alright, I'm feeling really frustrated and I just hope someone can understand these things that I am describing.
I had a lot of tongue tension before going to my current teacher who spent painstaking time working on that with me so that I no longer spoon my tongue. A lot of chest resonance come in a a result of this and the low and middle filled out first and was rich and resonant and not pushed. It was very natural, although I am called a lyric soprano with extension. I sing a lot of lighter rep, but I can't approach things the same way as a light lyric or coloratura. I had a strong, performable A below middle C. I had to work and work to add strength to my passaggio, which was always a trouble spot for me. I had a tendency to sharp in that area and had to work really hard to ground it and sing on my voice. Although, the more I was working on my voice the more I was able to open up passaggio and my whistle register got very strong. I think this may be confusing to hear because there is a lightness to my voice, but it is rich at the same time. It has a natural aggressiveness to it and a lot of body in the middle.

I went to a program and was told to straighten out my vibrato, use less appoggo and make passaggio very, very thin and pointed. By doing this technique even for a few weeks I completely
lost my chest voice and resonance, all my support and now my voice feels worse in passaggio. I felt I was definitely much more on the right track before and I never got fatigued, while now I do. I don't understand how altering a technique for such a short time can mess one up so much. I've been sick before and had to rest for a few weeks and was always able to get back on the horse no problem. Now, I feel like I am starting all over. Is this because my support got so weakened or what...and what does it sound like happened? Has anyone had a similar situation happen to them?

sounds like you aren't using chest balance but you are holding out of those resonators! Allow your voice to release into a more balanced vibration - you are probably holding too high to keep your sense of passaggio smaller. If you are getting fatigued vocally, then you definitely need to find a more buoyant and suspended physicality. Sounds to me like you are holding breath and muscle tension. Using less vibrato and less appoggio - for what? This on its own does not make sense to me. Feel free to email me further.