Self Harm?

Our youngest has a new trick.

When he is feeling as though he is not getting enough attention he hurts himself.

For instance yesterday our eldest was rushing to get ready to go out and slid down the stairs and hurt herself. She started crying and we gave her cuddles and comfort to make her feel better. Our youngest (who was still upset from being 'encouraged' to eat his tea (i.e. he didn't have dessert, but our eldest did.)), saw that he was missing out on some attention and bashed his head against the stairs and started crying.

We wern't quite sure what to do, we were a bit shocked. Also we didn't want to give him attention and reinforce the behaviour but then we couldn't leave him so upset. I went for the asking him what he had done in a kind way and asking him what was he thinking and then giving him a hug. He seemed to calm down.

Is this normal? Any ideas on what to do about it?