Depression can cause a person to reduce physical activity sometimes to the point of staying in bed or on the couch for a long period of time. Your muscles atrophy quickly.
"According to Michael O'Leary, a doctoral student in York's School of Kinesiology and Health Science, a week of total muscular inactivity can cause 24 percent muscle loss.".
"We are seeing more and more evidence of how easy it is to lose muscle, compared to how difficult it is to regain it," said O'Leary.
It may be you are not ready to take on a physical activity such as Aikido's ukemi.
I would go see a doctor that specializes in sports medicine about the problem.