21 month old twitching while sleeps/ before sleep

My 21 month old daughter just reciently started getting tremmors while she sleeps. It starts before she is asleep just as she gets sleepy and you can feel her body relaxing. She starts to randomly twitch all over. Most are mild though constant but every once and a while there is a big one that will scare her. I don't know if they last all night, but I held her for a 2 hour nap and she did it the entire time. I am really worried there is something serious going on does anyone have any information or advise. I have a appointment on Monday for her with her ped. should certain testing be demanded? She seems perfect other than this.