Feeling weird after a B12 shot is not uncommon and can be attributed to a few reasons. One possibility is that your body is adjusting to the sudden increase in vitamin B12 levels. This can cause temporary symptoms such as dizziness, nausea, or an overall feeling of discomfort. Additionally, the injection itself can sometimes cause mild pain or irritation at the injection site, which can contribute to the feeling of being "weird." It's important to note that these symptoms are usually temporary and should subside within a short period. If you experience severe or prolonged symptoms, it is advisable to consult with a healthcare professional.