How we lose our voice
You're familiar with this: you wake up in the morning and you find you've lost your voice. Maybe it was the shouting at the soccer match last night. Maybe it was a full day of teaching, or pitching to clients. Maybe, you've got a upper respiratory tract infection.
But how does that happen exactly? The main mechanism behind this is inflammation, and hence swelling. What's important to understand is that inflammation can have a viral or bacterial cause, or a mechanical cause (from trauma, or irritants).
In the case of a viral or bacterial infection, the best course of action is to visit a doctor to determine if antibiotics are needed, and to get any other accompanying symptoms treated. This is probably familiar to most people.
What most people don't realise is that oedema (swelling) of the vocal folds due to trauma or excessive voice use is very much related to vocal technique. Especially in occupations where you're speaking practically all the time (e.g. sales, front-line staff, teachers), this becomes even more of a risk. Continued misuse of the voice can result in chronic voice difficulties that become harder to treat.
the simplest solution
The simplest way to get better from losing your voice is literally to stop talking. If you sprain your ankle, you try not to walk. Likewise, if you're vocal folds are swollen from all the talking, shouting, and poor vocal technique, resting it will help it recover.
In case you're wondering, whispering isn't a good idea either. If you do need to talk, keep it short, and stop if you find yourself straining too much. Of course, instant messaging is another way to stay in touch without putting your voice at risk.
Proper voice technique (yes, there are safer ways to raise your volume) can really help you to project your voice in a safe, and efficient manner. Look for a speech therapist to help if you find that you keep losing your voice, or if you haven't quite found it after having lost it.