Meanings of nervous overstrain in English

There is nothing we moderns are more apt to brag of than the nervous overstrain of our life.

We were aged and weak from our drugs, dissipations, and nervous overstrain, and the thinning hair and beard of my friend had become snow-white.

For instance, the increase in diseases of the heart is often due to nervous overstrain combined with either too much or too little physical exertion.