I play Mr. Tech Support for my family, and camera/SD card related issues are one of the most common. Unfortunately, 99.9999999% are really just user error.
We need more details from you: When you say, “but today when I tried to upload them to my computer”, what do you mean? What is your process for getting the files from your SD card to the computer? Do you use a card reader or do you do USB from camera to pc? And when you “upload” them, what exactly does that mean? Do you use Windows’ built-in “import photos” feature or do you simply browse to them via Windows Explorer and just treat the SD card like any other drive?
To me it sounds like you probably accidentally deleted all of the photos while viewing them last night on the camera. There’s also the possibility that your camera organizes photos in some kind of folder format, so the photos are there, but they’re not immediately visible because you used some import feature or something. There’s also the possibility that you use some proprietary software to “upload” the photos to the camera. If that’s the case, all bets are off.