^^^ Finally. 50mg of diphenhydramine, or any similar 1st gen antihistamine is best . (12.5-25mg doxylamine, 3-4mg chlorpeniramine, and as mentioned, RX's are the best( hydroxyl one really, but promethazine is good too.
But generally, Zofran and the few other serotonin-based anti-emetics seem useless for opioid induced nausea(personally, I think they are ineffective, period).
And remember, a 30mg morphine tablet is almost certainly ER, he took it whole, that's why the effects are lasting so long.
And he's been taking them for a while now, which is why it's hitting harder, with chronic administration, oral morphine is 1.5-2x as potent as a single dose.
You'll be fine soon, take an antihistamine(low dose) if your still sick, otherwise time will heal.
(Edit; Didn't realize gravol was another brand name for dimenhydrinate(which is 50% diphenhydramine anyway.
Most people find H1's to potentials opioids, but in his case simple treating the nausea is top priority over salvaging a buzz that simply isn't there.