I have been inverting regularly (except during periods) for the past couple of months. And I must say my neck feels longer and stronger. And if I place my 4 fingers at the back of my neck, I can feel the nice curvature of the neck. I can invert upto 15 minutes in one session.
No headaches have happened since inversions.
I will keep you all posted if I can beat Ragweed allergy this season. I am eagerly awaiting it. If I cant totally beat it, I am pretty sure I will make it very manageable with my inversions.