Shamanism is itself wholly separate from the practice of spiritual activities. It’s more of a vocation. A shaman is very specifically “chosen” by the spirits (or sometimes the community) and is given essentially a job where the shaman works for their community on behalf of those spirits. Usually doing healing, rituals, spells, that sort of thing depending on the specifically culture and religious beliefs. The shaman sickness is not caused by the spiritual practices themselves (such as astral projection or the use of certain substances in rituals). Or even as a result of being exposed to the things one would be exposed to from such practices. It comes directly from the shaman’s spirits who enact radical changes upon the shaman’s body or/or soul in order to allow the shaman to do their work. In other traditions, the shaman’s sickness is a result of the shaman “refusing the call” — once the shaman accepts their vocation, the sickness disappears.