Ian decided to just put it down to temporary insanity.
Barbara had a hand clutched firmly under his arm and a bemused smile on her face as she helped him stumble clumsily through the corridors of the sunny Roman villa.
"That," she began, "was definitely not one of your best ideas." The smile hadn't left her face and Ian had a sneaking suspicion that it wasn't going to anytime soon. She was enjoying this far too much.
"Temporary insanity," he said, speaking his initial thoughts aloud. He concentrated on making his speech coherent and more or less succeeded, though his words were slightly more slurred than he would have liked. "We've all been idle for too long. Makes us do something raving mad just to break the monotony."
"Makes you do something raving mad, you mean. I can control myself, thank you very much," she laughed.
"That's because you're always in control," he quipped back teasing. The intended barb probably would have had a better effect if his feet hadn't chosen that moment to tangle themselves together. He pitched forward sharply and would have hit the floor face first if Barbara hadn't caught him at the last second.
"All right, that's enough," she lectured, her voice suddenly all business. "You obviously can't handle talking and walking at once. Not one more word out of you until you're tucked up in bed, agreed?"
It had started out simply enough. It started out with Ian being incredibly bored.
In hindsight, Ian realized it was really his own fault. He hadn't kept himself as active in the villa as everyone else.
Barbara had busied herself with cooking and daily visits to the market. Vicki usually accompanied her, eager to for any chance to explore outside the villa. The Doctor split his time between studying the surrounding plant life and Roman artifacts (though they had to keep reminding him to keep his anachronistic spectacles out of sight, so as not to arouse any unwanted attention), educating Vicki and getting into intense historical debates with Barbara.
And Ian - when he wasn't occasionally helping Barbara with supper or being lectured by the Doctor — just slept. Self absorbed and lazy probably, but during their adventures he was the one who usually expended the most physical energy… so the others graciously turned a blind eye and just left him to it.
Though after a few weeks, the inactivity was finally catching up to him. He found himself getting a bit stir-crazy, looking around for anything to break the status quo.
Challenging the Doctor to a wine-drinking contest, however, was probably not the best way to achieve this.
"Goodness, I don't think I've ever seen you this bad," Barbara remarked as Ian all but crashed onto the couch in his adopted bedroom.
"How was I supposed to know that he'd drink me right under the table?" Ian mumbled, face buried in the couch and voice still laced with inebriation.
Barbara smirked. "Well, that's what you get for playing drinking games with someone of alien origin. For all we know, alcohol doesn't have any effect on him at all."
Ian groaned in response. "That doesn't help, you know."
She giggled in spite of herself. "I know, I know. I'm sorry. You just lay there and try to sleep it off. I'll get you some water and set it beside your bed, you might need it."
She chuckled once more and leaned over the couch, planting a brief kiss on the top of his head. "Goodnight, you silly man."
With that, she made her exit and left Ian to his torment. Though Ian knew well enough from experience that he wasn't ever, ever going to hear the end of this.