A psychological disorder that can set in shortly after school is ended for the year. Symptoms can include boredom, lack of creativity, lack of energy, lack of effort, insomnia, and general physical laziness. If left untreated, some of the more severe side-effects can include paleness of the skin, obesity, and living in your mother's basement the rest of your life.
I was going to go running this morning, but school got out only a week ago and I just decided to sleep in. When I got up I didn't even shower and just sat on the computer for 5 hours straight. I must be contracting Summeritus!