What occurs in the body during trance can be scientifically verified thorugh a variety of means, in particular the direct current (DC) potential. During trance, the brian experiences electric charges, and can maintain them over time. The DC is a value that is reliable for measuring excitability and wakefullness in the cerebral cortex. The DC values will also register changes during sleep and meditation.
Trance, however, has a very different effect on DC measurements. In particular, rather than lowering the DC values and indicating a state of less activity, ecstatic trance, when measured by DC, indicates an overactive state, one which could be described as "more awake than wide awake" in terms of function. Combined with the measurement of theta waves (which are associated with deep sleep), overactivity can be measured as increasing significantly during periods of very vivid experience during trance.
Tensing and relaxing muscles can also have an effect on DC: tension increases DC while relaxation decreases DC values. These changes can last for several minutes, and relaxation can quickly drop the DC values, which shows a clear correlation between posture and trance. This may help explain why, when I move about during ritual, I find myself drifting out of ritual experience: the relaxation of some muscles when I shift my weight, change my posture, or swat at a mosquito is likely to decrease the vividness of my experiences.
Changes in bloodpressure are also known to occur during trance. There is often a drop in blood pressure in the middle of a body posture (interestingly, this change comes at the end of a trance state involving channelling). Adrenalin and noradrenaline levels also fluctuate, and changes occur in the levels of beta endorphins.
While not a lot is written on the physical body changes during trance, it is clear that some things do actively change: the state is not "all in the mind," and is, in fact, tied strongly to the body in a variety of ways.