DD (20 months) has started hitting herself on the head, initially it was once maybe twice a day but now it's happening several times a day. She often does it after I've told her to stop doing something (as if to punish herself) but she often does it for no apparent reason as well. Is this normal? I find it a little upsetting every time. I usually ask her to stop when she dies it but I'm not sure it's the right approach as it may be an attention-seeking thing? Anyone else had this?