First as with anything it's important to CALM DOWN, seriously as long as our brains are in overdrive no reasoning can be made. Second go to the doc, if your feeling like this might be major the only way to put that too test is to see about it and get help as needed. Now if it is in fact just anxiety then we can both breathe easy :-), bc I'm a little worked up with you here lol. I absolutely know how terrifying it is to be so unsure and afraid. Challenge those what ifs by saying what if? Whatever is wrong with you there is always a cure or treatment out there and I think those what ifs have us so shook because we're frightened of being hopeless, but there is hope.you just have to seek it .
Peace and blessings.. let me know how it goes