Guaifenesin
"Not long after taking my first dose of extra strength benylin for a persistant cold/respiratory infection, I became so dizzy I couldn't stand up and had to lie down. I closed my eyes and nodded off and woke up a while later feeling a little woozy but not dizzy. My head hurt the rest of the day. Did seem to help bringing up phlegm that afternoon. I think I would take a half dose next time."