I'm so glad that once you found this info that everyone helped you easily and quickly, that's a great start. First off, how old is your lo? As far as your questions:
What Happens if this is what he has?: What should happen is that during the x-ray they will watch your lo with different levels of thickness in a bottle (regular, nectar and possibly honey or pudding thick) and they will determine what thickness your lo is tolerating. You will need to buy a liquid thickener and thicken his bottles to that consistency. The younger he is, the quicker he will come to tolerate the new viscosity and have an easier time taking bottles.
How serious is it?: Dysphagia can be a small part of more complicated issues. But when dysphagia is your child's only issue, it's no big deal at all. He will simply outgrow it with age. We finally stopped thickening Luke's liquids around the time of his second birthday. Some outgrow it much earlier, and some a little later, but the good news is that they all outgrow it.
What can I do to help him until the appointment?: How long do you have to wait? I didn't used to recommend this, but now I do when people have to wait forever-go to the drugstore and buy a powdered thickener and try to thicken to nectar consistency. It may take more than one bottle for you lo to tolerate it (or he may immediately take to it and be fine). If you go a couple of days and notice no change, try the honey consistency. The directions should be right on the container.
What treatment does it involve?: Unless he has developed severe oral aversions and oral-sensory issues, the only treatment is the thickener and some follow-up appointments with the speech therapist to determine how he is doing. Your lo will outgrow it. If you start to give your lo baby food, for the runnier foods you should thicken them by sprinkling a little powder on them too and when you mix up cereal, make it thicker, more like applesauce versus making it super runny as they suggest.
Let me know if you have more questions, I hope you get your appointment soon!