What does the last part of this quote mean?

Question

Cultivate the habit of early rising. It is unwise to keep the head long on a level with the feet. -Henry David Thoreau

Answer 1

He is encouraging early rising.

In the second sentence he is saying that it is unwise to lie

a-bed too long.

Answer 2

Don't keep lying down.

Answer 3

He's talking about how it's bad to stay in bed where you're feet and head are on the same level since they are both on the bed.

In other words "Wake the frell up!"