Nightmares?

Hi, my daughter is 2 and has been a bit poorly over the past couple of days but keeps waking up from either her nap or at night screaming, shaking and in a right mess after clearly having a nightmare and i have to calm her down which can take ages, she clings onto me and doesnt want me to leave her alone. Its really awful to see her in such a state. I was wondering if anyone knows if this is a stage that kids of her age go through, she doesn't watch anything that could scare her unless In the night Garden Is scaring her! lol. I've heard of kids having nightmares but wasn't sure if they started so young.She has slept through since she was about 7 weeks old and i have never really had problems with her waking at night unless she is teething or ill but nothing like this. Any ideas? It is horrible seeing her like that but i suppose there isn't much i can do about it but comfort her but as i say just wondered if this could be stage kids of her age goes through? xxx