Mononucleosis, often called mono, is a viral infection commonly caused by the Epstein-Barr virus. It primarily spreads through saliva, which is why it's sometimes referred to as the "kissing disease." Symptoms include extreme fatigue, sore throat, fever, and swollen lymph nodes. It mainly affects teenagers and young adults, but anyone can get it. Most people recover from mono within a few weeks, although fatigue can linger for months. There is no specific treatment, so rest, hydration, and over-the-counter pain relievers are recommended. It's important to avoid contact sports during recovery, as an enlarged spleen can be a risk factor for injury.