Seeing some quotes not taking Maclin's mono seriously because they got it as teen and recovered quickly. Here's some stuff about getting it as an adult, which is quite another matter.
"Adult symptoms of mono include an overwhelming feeling of fatigue. It can take as long as months for your energy to come back completely. An adult with mono will experience the same symptoms that a child or teenager will experience, including fever, sore throat, swollen lymph nodes and tonsils, headaches, lack of energy and loss of appetite. They may also experience jaundice, stiffness of the neck, a rapid heart rate, and shortness of breath. The major symptoms will usually last for two to four weeks, but a full recovery for an adult may take months."
"The most important thing, if you are diagnosed with mono, is to slow down and give your body the time that it needs to heal. When people get mono as adults, they often try to continue with their routine. People need to understand that this virus can be quite debilitating and that they need to give themselves quite a bit of time to recover and to get back to their old selves."