Your gut and intuitive sense tell you that you may be heading into a few days of feeling run down, tired, and maybe even outright sick! In fact, you may be coming down with something that you have to either head off or at least lessen its severity. The key is to pay attention to that deep sense that something is changing, something is wrong. It just happened to me!
What did I do, and what do I do when it happens? Initially, I go to "battle stations" and prepare, even if it does not amount to anything. If it does, and you slide into a cold complete with a sore throat, congestion, cough, etc, you will at least be prepared.
First of all, I hydrate with water and lot of it, preferably filtered. I drink a full glass of room temperature water once per hour with a bit of lemon / lime squeezed into it. I don't count the ounces; I just note the appearance of my urine and look for it to run clear and often. I also take 500 mg of a chewable vitamin C with the glass of water. Make sure you get a brand that doesn't have sugar or fructose in it. Some people are sensitive to vitamin C and might develop loose stools. Great! You are cleaning out the way your body is designed.
Then, I make sure to get great chiropractic treatments to balance and stimulate my nervous system. Remember the chain reaction: Spine-Nervous System- Health and Healing.
Next I take extra vitamin D, magnesium, and omega-3 fatty acids: what I call the "Big Three". They are known to boost the immune system along with alot of other things. There are literally a hundred herbals, vitamins, and minerals you can take, however, I like to pare it down to the minimum. The omega-3's I take are in the form of fish oils or krill oil.
My diet shifts to crisis mode: eat only when hungry, eat light, even try a little fasting, even if it's only limited to the intake of soups, bone broths, steamed vegetables. Just for a day or two. Certainly no sugars, grains, or alcohols. Warming foods, even with a little bit of spice, stimulates the microscopic cilia, or hair cells, lining the entire respiratory tree to move mucous up and out, the so called "ciliary elevator".
Lastly, rest. Cut your schedule, take a hot bath and while you are at it check out the "wet sock" treatment in my "articles" section on this website. Baby yourself but if you have the energy, do things that feed you: light exercise, read, meditate. Listen to your body. It will tell you if you should or should not do certain things. Basically, lighten your load and heal.
Hope this helps!