At that age they do go through stages. I know DS2 has in the last few months gone through phases of being clingy, not clingy, really social, less social etc. I think it's probably a normal phase, probably brought on by her recent experiences. Perhaps you could use it as an opportunity to talk to her about emotions - you could try asking if she is scared of being hurt etc. I find that DS2 usually has a reaction similar to what you have described when he is feeling something he can't communicate. I am hoping by talking to him about what he is feeling (even though he can't respond in words LOL) that I am helping him to deal with his emotions as he gets older.

FWIW, it does get easier as they get older and can explain how they feel. DS1 is now really good at telling us what he's feeling and it makes life much easier!