The three main things the body needs when singing are rest, proper diet, and plenty of water. 

Colds

• If you feel a tickle in the throat or a cold coming on, manage symptoms quickly before you have a full-blown cold. It might take at least two weeks for recovery otherwise.
• I have found it helpful to take up to 2,000 mg of vitamin C and two capsules of echinacea every four hours for four days with plenty of water. This has usually alleviated my symptoms within that time. Colloidal silver is a natural antibiotic that also seems to be helpful.
• All of the above should be combined with getting plenty of rest.

Fatigue

• Singing is an athletic event. We need the muscles for singing to work properly. Because we have exercises to condition the singing muscles, they may get tired. Therefore, get plenty of sleep. This will allow the muscles to heal and rebuild.
• It is harder for the muscles in the throat to work properly if they are tired. Therefore, take a vocal rest if necessary. Three to seven days of no singing or vocal exercises would be sufficient. 

Listen to Your Body

• Be mindful of what foods your body can handle before singing or to which foods your body is intolerant.
• Allow yourself time between eating and singing - two hours after eating a meal and one hour after eating a snack would be sufficient. We want to use your energy for singing instead of digestion.