Vomiting in toddler

[Anxciousmama02]

Hi, my 21 month old randomly vomited in her sleep on Friday night (but didn't wake). Seemed fine the on Sat, but a bit off her food. Sat night she vomited again. She had slightly lose stools on Sunday but Sunday and Monday she seemed fine, just no appetite. She has now vomited up all her plain pasta that she ate. No temp and seemed fine after. Any thoughts as so what it could be?

A bug.
The rehydration stuff is great. I start with giving small syringes every 5 and then 10 minutes and building up so that she is getting fluids etc