Had to shake toddler awake

About 5am this morning I checked on my daughter like I do every night. I put my hand on her back to make sure she is breathing but this morning I didn’t feel it. I shook her multiple times and yelled her name and she was limp. I picked her up and flopped her over and she started stretching and moving around. I abjut had a heart attack 😭 could she have just been in a deep sleep? We went to the creek yesterday so she was in the sun half the day and we didn’t get home until late. Maybe she was just that tired but it freaked me out!!