My SIL went Teneriffe with a really bad cold/flu a couple of weeks ago. I don't want to worry you Tilly, but she said it was the worst journey she'd ever had. But she said that it cleared once she got there and she had a great holiday.
Just dose yourself up with as much as you can hun and try and sleep as much as you can on the flight. 24 hours is a long time in the life of a cold, so you should hopefully start feeling a little better tomorrow anyway.
