When we get a sick, we typically get PAIN, SWELLING, REDNESS, MUCUS, FEVER, and FATIGUE. Below outlines the process of an infection and how the body responds (note the arrival of each symptom (those listed above in CAPS) in the following explanation). The steps outlined below show why the symptoms associated with a cold/fever/flu are normal reactions of the body and are all apart of the healing process.
Bacteria enters the body --> infects the mucosal lining of the throat, lung, nose, etc --> macrophages and dendridic cells of the immune system (who travel around the body looking for invaders/pathogens) --> they start attacking the bacteria --> necrosis (i.e. death) of bacteria and even some healthy cells --> PAIN
Macrophages and dendridic cells start releasing cytokines (IL1, IL6, and TNFalpha) when the encounter the bacteria --> irritate nerve endings --> PAIN
Cytokines notify the hypothalamus (gland near the brain responsible for body temperature) --> increases the set-point temperature of the body --> FEVER
Bacteria also secretes toxins (endotoxins) --> trigger the hypothalamus --> also increases the set-point temperature of the body --> FEVER
Bacteria secretes more endotoxins --> irritate nerve endings --> PAIN
Dendrites and macrophages meet the bacteria --> ingest/pick-up bacteria --> transport to lymph nodes to notify more immune system cells (T cells) that the body is under attack --> lots of activity in lymph nodes --> SWOLLEN lymph nodes
Cytokines recruit more helper cells (lymphocytes) --> lymphocytes attract vasodilators (chemicals that dilate vessels) --> dilate the endothelium/vessels --> increase blood flow to the area --> blood accumulates in the area --> REDNESS (blood gives color), SWELLING (blood is fluid), and HEAT (blood carries heat)
Vasodilators also increase the permeability of vessels in the area --> causes plasma to leak --> more fluid in the area --> SWELLING
Increased permeability of the vessels --> white blood cells (neutrophils and macrophages) leak into the infection site --> attack bacteria --> lots of dead cells result --> MUCUS (or phlegm/exudate/white patches)
Fever changes body's energy burning (metabolism) --> makes the body slow-down and want to rest --> FATIGUE
Fever --> directs blood to the core of the body and increases heart rate --> more blood (and thus more white blood cells) to the infection site --> more REDNESS, more SWELLING, more MUCUS --> heal faster
Fever --> triggers the production of more healing enzymes, more antimicrobial enzymes, and prevents the bacteria from reproducing (the high temperature breaks them down) --> continues the fight --> more SWELLING, more PAIN, more MUCUS --> heal faster
...and this is why we feel the way we do when we get sick. Every symptom happens for a reason! It may feel awful, but you'll heal faster if you let nature take its course and put up with the FEVER, REDNESS, SWELLING, FATIGUE, PAIN, and MUCUS.