The Purple Parasite

This parasite is a mite, a small, purple insect-like creature with a hard, shell-like exoskeleton. It is roughly the size of a grain of rice and is barely visible to the naked eye. Its body is covered in tiny, needle-like hairs that allow it to grip onto surfaces and crawl quickly in search of a host.
This mite is attracted to magic, and it can sense even the slightest magical energy emanating from a living being. It will seek out those with the most magical energy and attach itself to their skin, using its sharp mandibles to pierce the skin and feed on the magical energy within.
Once attached to a host, the parasite mite can cause a range of negative effects. In the short term, the host may feel weak, dizzy, and disoriented as the mite feeds on their magical energy. In the long term, the mite can drain the host of their magical abilities, leaving them powerless and vulnerable.
Unfortunately, little is known about the origins of the Purple Parasite mite. Some magic users take precautions to avoid coming into contact with them by casting spells to repel them.
(They can make you feel like you still have all your magic)