I filled my mouth with Robitussin and swallowed it...?

My mother gave me so Benedryl (or however you spell it) then I was stupid and didn't wait for it to kick in and filled my mouth with Robitussin and swallowed it, not realizing what it could do. What could happen? I'm really worried that if I fall to sleep tonight, I won't wake up in the morning (I'll be dead). Could this happen? If not likely then what could happen?? I am super stressed