Parasitical energy theory

  There are two levels of parasitic energy exchange. The energy given off naturally - the excess is the granom. The natural 'vampiric' instincts of the individual is the krenul. When the krenul is large and the granom is low, vampirism with a loss of vitality to the target often occurs.
  In sickness of the vampiric tendency of krenul can increase in an attempt to speed recovery of the person. This is often unhelpful as the energy cannot be properly filtered and unless a source is pure this will make things worse. When there is no trouble, the krenul acts as a recycler of sorts, to recycle excess granom energy of others to increase the flow of energy in the environment. Troubles wit this only occur when the krenul instinct gets too 'greedy' for more energy than the granom generated, as in sickness. The krenul will attempt to draw in the active energy of another, causing an energy loss from the target. This event is widely perceived as psychic vampirism and an attack.
  Extraverts use the granom-krenul action most effectively and they naturally have a larger granom and krenul. This is how they are energized by others, as their energy is recycled allowing for a more in-depth sharing of concepts and ideas. Introverts naturally do not use the system - they have a smaller granom-krenul vampiric system as the energy is usually recycled themselves when they consider the events and ideas of the day. This is also why introverts can feel drained near too many extraverts as their vampiric systems are not developed enough and usually get drained by the extravert krenul. While this is fine for the extraverts, introverts do not generate enough granom and their active energy can be drained as a result. This can also explain why extraverts have more trouble sharing ideas and concepts with introverts, as they have different methods of sharing information. Luckily these are not set things, as it is easy enough to change the granom-krenul levels using simple techniques, as many have already found - particularly psychic vampires.
  Psychic vampires can be erratic or ordered. The erratic psy vamp can occur when there is an imbalance of energy in the person and krenul activates to replace the energy being lost. As the person lacks discipline or judgement to rein in their energy output, they must take in much more energy just to retain an equal balance of energy. These erratic vampires are often unconscious, and can spontaneously stop their vampirism once their condition is healed or righted in some way. Erratic vamps can also be lost souls seeking other energy sources to find solutions to their conditions. Unfortunately, granom and drained energy is very unordered and takes willpower to convert it into untainted, usable form. It can be used in raw form, but there are side-effects. The problem that occurs to the erratic psy vamp now is that there will be predispositions to the energy they take, causing mood imbalances, unstructured thought, thoughts from the individual that the energy was taken from, and others. This can change the person with unforseen consequences.
  Ordered psy vamps are potentially more dangerous than the erratic vamps as they are nearly always conscious of their actions. They use techniques and a measure of control unseen in erratic vamps - so that almost no energy is lost to them as granom, and this can also be a method to detect them. Be aware as this detection could also confuse the psy vamp with an extreme introvert. The ordered psy vamp has a huge krenul and the ability to purify the energy before they use it to generate desirable effects.
  To defend against the energy-draining vamps, use a wall shield to prevent others from accessing your active energy. By imagining a wall the color of your choice surrounding you. Granom will not be affected. Granom is useful in its own way but can also be used as your own energy source - particularly if you are a natural extravert. Techniques on changing your output of granom and krenul will come later, or figure it out yourself.
  And also, when a paid vampire comes to you, it builds a link to and in your stomach (aurally) that causes you to feel sick in your stomach, and sucks your life energy from your source of 'intent'.
  And this can cause many problems which can lead to worse positions than health problems or energy loss.

Idea by Caz and little additions from Libertine and Skyhawk