Re-occuring, unintentional booger swallowing

For the past few months, I have had a re-occuring problem where out of the blue, the back of my thoat will feel like it's having an allergic reaction to something, and then within a couple seconds I'll feel what seems to be a large booger, covered in mucous, making its way down. It's disgusting, and it will take me by surprise, happening anywhere at anytime, with no apparent provocation.

I'm lucky when I can get someplace fast enough where I can cough it up. It's usually a large, harder version of a booger, whitish or yellowish in color.

What is causing this? How can I get it to stop? Is this an indication of something serious?

[friggy]

It is possibly a minor sinus infection, and the chunks are a slow form of post-nasal drip.  It may or may not be a result of a fungal infection, if you are not otherwise congested.  If you are lucky, it is in the maxillary or ethmoid sinuses, in which case you can wash out the infection with a Neilmed Sinus Rinse, now available in most drugstores.  Or just go to an ENT, which is what I should always suggest.