Where's the imperative?

Question

When I read Guillermo's answer to Saramallorca, Unless you meant I sit happy. You could say it if you like the chair a lot. I laughed and thought it would be a wonderful motto to have on a pillow for a chair for a guest to sit on. Something like Sit here and be happy. But when I looked up the conjugation for sentarse, there was no imperative. Why not?

Answer 1

The conjugations are all for the root verb, sentar. It's the same conjugation, with the addition of the reflexive pronoun on the end (if it's a positive imperative).

Answer 2

Sit here and be happy ---->Siéntese y sea feliz