Kriya practices are not for everyone; if prana is stagnated at one place, it might lead to apathy, sluggishness, lethargy, dullness, excess mucous, sore or stiff limbs and body, back pain,, aches and pains, asthma and various other dysfunctions.
At the subtle level, it is pranic stagnation, and at the gross level, it is toxin formation. These toxins inhibit or suppress natural mechanisms and lead to chronic disorders.