My two year old has been so emotional lately. I've seen that she's cutting her back molars, so that's understandable but also it must be developmental as it's sometimes when it's about a toy or simply being told no.
Tiredness doesn't help, and afternoons are worse, she refuses to nap as tries to keep up with just four year old big sis.
It's just stuff like the piercing scream, feeling groggy and saying she's always tired.
Just changed the past few weeks.
I think the main cause is teeth as she has cold symptoms with it too. Horrible seeing her like this.
Been off her food too 
I know each child is different, my eldest girl did have these moments but not as bad.