It is because the slate absorbs heat quickly and dissipates heat quickly, and it is easy to absorb heat from the back. "The back is Yang", and the Du meridian runs through it. Du meridian is an ocean of yang, and the absorption of yang can easily cause Du meridian diseases, such as low back pain and rheumatoid arthritis.

Sleepless board in autumn:

It means that people don't sleep on hard beds in autumn. In autumn, the climate is dry and the weather turns cold. Sleeping on a hard bed is easy to cause local qi and blood stagnation, which makes people feel quadriplegia more easily than in spring and summer.