Suddenly yesterday my almost 21 month old ds seemed to develop extreme separation anxiety. My MIL who lives abroad but who he sees fairly regularly came to visit and he was literally petrified of her, clinging to me, crying, not even wanting to look at her or touch her the whole time of her visit. I thought this might just be her but today I have been to see my mum and he is suddenly terrified of her too. He sees my mum regularly (several times a week) and has never been like this before. He is acting like she is a total stranger. We have had quite a few different relatives visiting recently (but none staying with us) so he has seen a lot of different faces in the last few weeks but it has literally been so sudden this change in behaviour. He is normally a very friendly, happy boy who is not scared of strangers and goes to explore on his own (in full view of myself). We even had a playdate yesterday morning and he was fine, his normal self. What could have caused this? Has anyone experienced anything similar? Could he be ill?