DD (16 months) suddently upset for no reason - help

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DD is full-time at nursery, and they spoke to me today, saying that last week she seemed to get very upset quite often for no apparent reason. For example, she would be just playing by herself, and would suddenly scream or get upset.

I am a bit worried; I didn't notice this happening over the weekend, but am concerned that it might be a health issue. Or is this some sort of phase?

Help!

teething? coming down with something? 16 months old is a v emotional time.

Thank MrsJamin. I did wonder about teeth... nothing apparent, but will have another look this evening.

DD has definitely become more noticeably aware generally i.e. is slightly worried about insects and the knot-patterns on the wooden floors, so perhaps it's another evil I haven't quite worked out yet...