Why are some of my contacts were deleted from my iPhone 5s?

This morning all my contacts were fine, but when I went to send a text message this afternoon, I noticed that some of my contact names had disappeared and it was just their number in the message thread. As I looked through all the contacts that had just disappeared from my text messages, I noticed that all of them had been added since I got my new phone a little less than a year ago. Any contact I had on my old phone was still there. I turned my phone off and on, but it didn't help. Then I went to check if the contacts were still on my computer in the iCloud, and they were gone from there, too. How do I get them all back?