sudden weight gain following car accident

Okay, I wanted to know if I am alone in this or has it ever happened to anyone else. I can talk about it now because it's over and not worrying me anymore.

Last month I got rear-ended in my van and sprained my back. I went to the ER and was given pain killers and muscles relaxants. Not a serious injury, I was just very sore all down my back. The next day, I felt funny and when I weighed myself, I was 133 pounds! Normally I weigh 115. This had me thinking swelling or internal damage or something so I went back to the doctor and they were surprised at the weight gain, which didn't make me feel any better, but they had it written down right there, 115 on Saturday, 133 on Sunday. 18 pounds in 24 hours, no out and out signs of edema, either, the doc said. I thought I looked puffy around the tummy and back, but he said it would also be in my hands, feet and face.

They took a bunch of x-rays and did a bunch of blood tests and nothing unusual came up. My weight went back to normal over the next 2 weeks and it's been almost 3 weeks since coming back to normal weight and I'm fine. Nothing like losing 18 pounds in 2 weeks to make you appreciate your regular body, though, that's one good thing.

Why did I gain weight? No edema, no long term problems, no infections, the doctor never figured it out. Has this ever happened to anyone else? Does my doctor just not have a clue what's going on? And the weirdest thing was, all my regular clothes still fit me during this time. Is this really so abnormal? I thought it was torso swelling, like as if I had stubbed my toe or banged a thumb, but he said it doesn't happen in the body like that, it shouldn't have stayed in one area.

It really freaked me out, though.