Some folks really do get fairly mild cases and only feel tired and run-down and just think it's exhaustion, then later mono is reflected in their antibodies after bloodwork. It just varies from person to person. My son never knew he'd had it till it showed up later on his bloodwork. He just thought he was tired for about six weeks.

For me personally, it was a mean thing. I had a hideous sore, blistered throat and swollen lymph nodes, fever, aches. The works. I think some immune systems must simply stand up to it better than that.