Sleepwalkers, or the Green Plague, a new kind of ravenous undead for horror (and fantasy) roleplaying.

First of all, let's establish a scientific basis. Not needed for fantasy or supernatural horror per se, it's still interesting.

In the real world, 'sleeping sickness', or human African  trypanosomiasis , is a disease caused by parasitic protozoa of the genus Trypanosoma . There are a couple of varieties, mainly differing in how long they take to really manifest severe symptoms. The disease is transmitted, primarily, by the bite of the blood sucking tsetse fly. In the early stages, one suffers joint pain, fevers, headaches and muscle pain. In late stages, the symptoms include difficulty staying awake, confusion, a shuffling walk, then finally coma and death. The symptoms are said to include general 'sleep disturbances' so sleepwalking is not out of the question.

Next up, these parasitic protozoa are plantlike in some ways, and belong to a phylum of life called the Euglenozoa. Euglenoid algae, which are also in the phylum, are photosynthetic.

Now. Imagine a mutation, or even just the discovery, of a new protozoa that, after a short while, causes severe brain damage and sleep disturbances. Victims turn green, of course, as chloroplasts build up in their skin. In this case, once the disease causes the infected person to fall asleep (especially after they have entered the coma stage), they sleepwalk, and attempt to infect others by biting them. They also still have normal human needs, so the need to propagate the parasite via biting is conflated with human need for food, and thus victims who die are eaten. Standard zombie/ghoul behavior. But here's the twist. The protozoa is photosynthetic, causing the infected to sleepwalk during the day to soak up the sun, and rest at night to conserve energy. In addition, if the infected can get enough nutrients (by eating people or animals), the body lasts longer, but they can live a very long time just by getting enough water and sunlight. They also sometimes eat dirt. The parasite is still carried by biting flies, and can infect animals as easily as it does humans.

Being a photosynthetic living organism, the 'undead' produced by the parasite would not be vulnerable to sunlight or what D&D calls radiant damage. They might even be healed by it. The infected might (or might not) be vulnerable to necrotic damage instead.

Thoughts?