I realize that this is a fairly common occurance, and in my experience has been regarded as a vocal dysfunction... Last night, after singing some high-tessitura pieces (Bizet's 'Le Papillon' and Mozart 'Et Incarnatus Est') I found that high notes which normally are somewhat challenging -- Cs and Ds -- were truly effortless. As I imagine they should be, since I'm a coloratura soprano...
But my lower register was totally gone. I could reach the D above middle C with ease, but the low Bb in the Mozart was very difficult.
Similarly, when I work harder on warming my lower register, my high notes start to crap out and my whistle register is almost gone (F6 is a struggle, when some days I have E7).
I feel like I'm having to take a range of two-and-a-half octaves and move it up and down the piano, sacrificing either the bottom of the top of my range.
I might think that perhaps this is caused by muscle tightness? Perhaps the 'close' and 'stretched' position of my muscles is making it hard for them to take an 'open' and 'relaxed' position for low notes, and visa versa??
I have always thought that having a solid lower register -- even when singing high tessitura -- is important for having a muscularly balanced vocal mechanism (proper opposition), but is it normal for a high coloratura not to have much in the bottom?