I think I have a cold. Battling anxiety and/or depression, and then getting a cold, flu, or other infection is the worst. After reading the following article, it's clear why. Already a depressed brain has a lot of abnormal activity of neural circuits, and then with a cold the body releases these proteins. The proteins are called cytokines and in short, they signal to the brain that you're sick. They do a lot of good, but they also make you feel sleepy, you lack concentration, and of course, you will feel depressed.
Here's the article I'm referring to: https://www.rd.com/health/wellness/common-cold-and-the-brain/
That happens to be the one I read first, but there are all kinds of articles on this topic. Here's another: https://www.psychologytoday.com/us/blog/urban-survival/201502/the-surprising-psychology-the-common-cold
The next time you are sick, now you'll know it's just some proteins making you feel even worse. But, don't be too mean to them, they are helping to heal your body. 😉