Unresponsive toddler who stopped breathing

Patient: My daughter is 3 yrs old. And last night I woke up at 1am for no real reason. Went to check on my kids. Found my daughter not breathing. I tried to wake her up by calling her name, touching her shoulder, did the sternum rub. NOTHING. So I started to panic and picked her up bunder her arms and began to shake her and scream. Then she wakes up and looks at me, exhausted. What the heck happened? She seemed fine and was a rosey pink color. I let her go back to sleep but I didnt sleep very well. Kept waking her up. What do I do? What could of caused this?