Declining skill or fitness level from taking a break from exercise is formally referred to as?

Principle of Reversibility is the decline of skill and fitness level due to taking a break from exercise or being inactive.

It is called such because all the result of hardwork and labor done to achieve and maintain one's skill and fitness level will be reversed because said fitness regime is not maintained; making the body lax, eventually declining in skill performance and fitness level.

They probably don't understand either 1. what the nightmare is about or 2. his anxiety and stress