I have this experience and since I am practicing quite isolated and have no one to share them with, I thought maybe it's worthwhile to share them here.
I am practicing Vipassana, have been on two courses and currently practice twice an hour daily. During retreats I had experiences of gross solidified and sometimes irritating sensations throughout the body, these tended to come in waves and would vanish part by part if I remained equanimous.
Off retreats in my daily practice, I feel some gross solidified sensations too, but merely in the region of my head. They tend to manifest on my face and entire skull and have the characteristics of worm-like structures moving around, sometimes made of water, sometimes made of ice.
As I try to always be aware of the sensations of the body when not meditating, I experience these solidified sensations in and on my head almost during the whole day. I try to be as equanimous as possible and mostly do not react to them. At times these sensations become more gross and solidified and this results in me feeling not in tune with myself, I become less clear-minded and feel like my brain is freezing and I can't access some parts of it. For instance, sometimes I can't come up with words that I want to say. Another funny things is that often when I scan through and past these sensations, my head or my body tends to move or jerk in the direction I am scanning.
These experiences are occuring for a month or three now.
If someone here has had these experiences or has knowledge of these experiences I would very much love to hear from you.