unfortunately i know nothing about the crusades... but i have read a bit about ergotism (caused by a hallucinogenic fungus) and it's some freaky stuff! I think the first documented cases of ergotism were on Barley in ancient greece (no corn in Europe until after contact with the Americas) but the fungus also grows on wheat so they could have def. been tripping on it at some point before/during the crusades.
Also, not to digress, but on the subject of visions and war- i have heard a lot about Joan of Arc possibly suffering from what would be diagnosed as schizophrenia today. Any thoughts about the role of mental illness in religious visions and "messages from god"?