Hi there Sommerclark,
I understand that your iPhone 5s randomly turned black while you were using it.
Here is a great user tip from our trusted Apple Support Community members:
What to do if your iPhone or iPad will not turn on
Or if you rather prefer, you can also read this knowledgebase support article from Apple:
If your iPhone, iPad, or iPod touch won't turn on - Apple Support
Whichever one you'd like to read is up to you. Both are great, but you may find one may provide better instructions or one may help you completely resolve your problem.
Hopefully this helps you!