Bummer. Sounds like it's time to call a plumber, in my opinion. Sounds like maybe there is a clog in the line, and it's best to get a pro to help with that.
unless you want to invest time into watching YouTube videos and purchasing a plumbers "snake" ... it would be wise to call a Pro. Especially if your downstairs is a basement
Marisa, in case you decide calling in a Plumbers, then you can find a professional here on HT- http://www.hometalk.com/?industry%5B%5D=19&search=contractor
have you tried a few buckets of very hot water with squirt of dish soap?....most toilets clogs are not 100 % and after a few minutes will drain down...wait for it drain back and add some very hot water. This has worked for me on a number of occasions when my 12 year old daughter goes a little nuts with the TP
It sounds as though the plug may be a bit further down the line then just near the toilet. If KMS idea does not work for you, you may need to snake the drain line further down the pipe. The toilet auger will go just a bit past the floor bend and that's about it. You will need to locate the clean out fitting that should be just up hill of the offending toilet and snake from that point on.
Using a pro on this however may be a better idea if your not comfortable in using a power snake. Which by the way can be rented. The pro will not only snake out the issue for you, but perhaps even be able to use a camera to check the inside of the plumbing to be sure that there is no issue inside of the pipes that may cause this to happen again.
If this is only a once and a long while issue, It as KMS said most likely was a over use of TP or other paper products that has caused this to happen.
Many years ago I had a tenant that had the same issue. We snaked both main and the toilet lines. Every time we used the closet snake in the toilet it worked. But only once then plugged. After replacing the toilet and breaking it apart to figure out why it kept stopping up. We found a compact mirror in the bowl drain line. It fell in such a way that it acted as a little flapper. When we pushed the snake in it opened up and allowed one flush to occur. But as soon as the next flush happened it would flip over and block the water.
Ages ago I cleared a toilet of tube of Heavy duty hand cleaner...it was a bit smaller than a basic tooth paste tube. I had gotten wedged in the S bend of the toilet but out of sight from the bowl.