What happened

Start-up Israeli X-ray maker Nano-X Imaging (NNOX -5.40%) -- a recent IPO stock that had already doubled off its IPO price in just its first eight days of trading -- had an even better week last week. Over the course of four straight days of gains, this company that's aiming to upset the business model of other medical device makers by providing X-ray hardware as a service climbed another 76%.

Today, it's giving a lot of that back. Nano-X stock plunged 14.6% through 12:30 p.m. EDT. 

Chalkboard drawing of stock chart arrow going up being erased and pointing back down

Image source: Getty Images.

So what

The collapse comes despite the company reporting no bad news of its own, nor suffering any negative analyst reports (downgrades, price target cuts).

So why is Nano-X stock going down today? Possibly -- simply -- because it went up last week.

Consider: Right now Nano-X is a "story stock." It's a good story -- promising to manufacture X-ray machines and distribute them to doctors for free, taking as its compensation instead a cut of the fees charged for taking images with the machines. The company even has proof of the popularity of the concept -- a deal signed with SPI Medical last week, to distribute and share the revenue for use of 630 Nanox Systems in Mexico.

Now what

That doesn't change the fact that Nano-X has no revenue today, much less profits. It's also worth pointing out that even the SPI deal isn't quite a done deal, and remains dependent upon receiving "local regulatory approvals and acceptance test clearance" before it can proceed.

Potential hiccups like that one could still derail the stock's rise. Investors who are already sitting on a two-bagger -- or more -- in Nano-X stock already may be wise to take the money and run.