Most interesting. I've participated in a lot of group chanting and never heard this happen, so it may have something to do with the particular sutras or that particular group of people.

Chanting is very revitalizing if you get on with it and do it...just as is regular singing...and the energy of many people in a group heightens the experience. It's good for the physical system, the emotional system, and the spiritual system too (if you accept that there is such a thing).