What would or could happen realistically if a person swallowed a alka seltzer tablet whole or two at that?

i'm just curious cus i did the foamin at the mouth gag on some frends at a party once and i almost swallowed the whole tablet but coughed it up lol. jus curious wat could've happened if i had swallowed it or say played one on my friend like crushin one up in some munch some how lol jus playin...