Courtesy of BayouBlonde

Sadly, your little family members will become sick at some point in your game. You may notice their status message will become "A little bit sick" or perhaps something worse. You may also notice that they will cough, sneeze, hiccup, fidget anxiously or tap the screen for your attention. It's time to play doctor!

If you get a 'sick' status message and do not know the symptom, pick and drop your little person repeatedly until they display the symptom (cough, sneeze, etc.) Their status message will also tell you the symptom ("coughing", "sneezing", "itchy"...)

After you discover the symptom, you will need to purchase the medicine to cure them from the store and drop it onto your lil peep. Most of these will be self-explanatory, although the medicine names sometimes use 'medical' terms that may be a bit confusing.
Coughing
Sneezing
Headache
Itchy
Sore Throat
Upset Stomach
Hiccups

Sometimes one of your little family members will develop an infection. Infections will cause them to become sick again and again and their health will not recover as quickly, leaving them in a weakened state. If you can afford it, I recommend a physician consult be done if you notice the same little person has come down with a second illness soon after you cure the first. The physician consult will diagnose the infection (if there is one) and will tell you which antibiotic to use.
Penicillin is an antibiotic given by mouth. Vancomycin is an antibiotic given by injection. These generally should not usually be given unless an infection is diagnosed by physician consult. However, if you are low on cash the theory posted in this thread might help. I've summed it up below :


After you have administered the correct medicine, you should check their health and energy levels. In addition to the usual 'healthy' activities (exercise, regular meals and plenty of sleep with the game closed) the store offers some items that can give a health boost.


Most often, after curing an infection with antibiotic, your lil person will become very tired. You can encourage taking a nap, going to bed and using the hammock to recover energy. All of these activities must be completed before the game is closed to achieve the result. If the sick person was an adult family member and you need to get them back to work as soon as possible, the energy drink from the store can be used, if it is available.

TIP: I usually watch the store for the items listed above and try to keep one of each in the tool tray to be used in case of illnesses.

Illnesses can also affect their happiness levels. If they become very unhappy, try setting them on activities you want and praising them or giving them gifts from the store (including groceries,) or house upgrades and candy (remember that candy will also work as 'praise' to encourage them to repeat whatever action they are doing when you give it.)

If an illness is not treated right away, it can spread to other family members. Once you find and treat an illness in one lil peep, it's a good idea to check all the others to make sure they have not also become ill.

Good luck keeping your little family happy and healthy!