There are three forms of need: cyclical, induced, and battleprep. Cyclical is involuntary, caused by the normal buildup of egerin, since that hormone cannot be metabolized alone. A warrior's cycle length is individual, and can vary from five to eight days. If the egerin buildup is not interrupted by combat or sex (both of which stimulate adrenalin production to levels that allow interaction with egerin and permit it to be metabolized), about two-thirds of the way through a warrior's cycle he begins to experience heightened sensitivity, both physical and mental. This is the pre-need stage. Need itself begins as further-increased sensitivity that could be described as irritability, at which point patience and self-control are not among the warrior's strong points. This stage, as a rule, lasts for about a day; it is not dependent on the cycle length, and is what is called active need. If it is not satisfied, the warrior starts going into overload; all body systems become hyperactive, and the effect is one of multiple stress diseases. Untreated overload lasts about two days. The other two forms can be undertaken voluntarily at any stage short of overload. Induced need is the sexual form, stimulated by arousal and manipulation of the need gland. It results in heightened sexual ability and greatly increased fertility; if the warrior's partner is in her fertile period; conception is almost a certainty. If induced need is not resolved, it will abate on its own since it involves only the reproductive organs, speeding the warrior's cycle slightly--though the egerin fluctuations are quite uncomfortable to the warrior. Its resolution results in aftersleep, a near-comatose state that lasts for several hours. Battleprep is the combat-oriented form of need, induced by mental and physical concentration. Unlike induced need, battle-prep involves the entire body; unless the warrior goes into demanding combat within an hour or two, he will go into overload and die. As this is well known, a warrior will prep only when combat is imminent. Battleprep is often referred to as a berserker state, but that is only partially correct. The prepped warrior is only marginally, if at all, aware of pain and wounds; blood clots quickly to minimize loss; speed and strength are heightened on the same order as that of someone of average strength who can suddenly lift a car to save an infant. Beyond this, however, the berserker analogy breaks down, because the warrior retains his full intelligence and judgement. This combination makes a battleprepped warrior one of the most dangerous beings in the known universe.