When I first read this I thought of Sensory Processing Disorder -
http://www.sensory-processing-disorder.com/
And we have a very experienced parent who is the CL here -
http://www.medhelp.org/forums/Sensory-Integration-Disorder-SID/show/1396
who has a son with SPD and will be very helpful with questions.
However, SPD is something that (I think) does not suddenly appear.
Take a look at the first link for all of the possible symptoms and see if he also has any of them - like sensitive to textures, sounds, light, etc.
It may well be that this is a reaction to the choking and that particular thing can be dealt with.
I was worried about his anxiety symptoms. However, he is only 6 (probably in first grade) and with two younger siblings. That alone is/can be very anxiety producing. I've seen it happen on this forum many times. The CL on the SID forum referenced above, Specialmom, son at age 4 was a mess (to put it nicely). He is doing great now thanks to the proper intervention. My point is that I think that if your son has SPD, you would have noticed it sooner - but I am not the expert here at all. That is one reason to check out the first web site.
So lets go with the possibility of the choking being the cause. I say this because if he has SPD there are numerous other things to deal with. Although, the food sensitive would also probably work here.
Main thing is to slowly introduce chewable foods back to him. Not at dinner, but during the day, bit by bit. Maybe something like a single apple slice. Tell him to chew it 15 times and wash it down with water. Point being you need to let him practice with a safe food and just a little bit of it.
Get him involved in counting how many times he chews. Try different foods. Oatmeal, bananas should be no problem. Actually, try a single jelly bean and have him chew it up really well. I think (hope) he just needs to regain his confidence.
Now, if you check out the SPD site and that rings bells, then you definitely want to contact Specialmom.
Hope this helps.