For the last two weeks, I have experienced extreme fatigue. Normally, I work out 3 to 4 times a week, or play tennis. I am 58 years old. I always have high energy, but recently, by the afternoon I am plagued with chills and just wanting to stay on the couch. I have had headaches also. I do have a slow thyroid, and have been on medication for about 2 years. I also experience feeling extremely sluggish when trying to get up in the morning. Any ideas?