Depression is an illness that can sometimes cast a dark shadow over our memories. Depending on your mood you may not be able to come up with a good memory. Or, depending on your mood, you may not be able to recall anything good about a happy memory. Depression can do that to your memories.
I was going through a stressful time in my life (divorce), but coping, or so I thought. One of the ways I dealt with stress was through exercise, especially walking. One day, while on my walk, I felt like I could not walk as fast as usual. The only other time I remembered feeling that awful was when I had anemia. So, assuming that it was the same thing this time, I went to my doctor.