It means you have plenty of money so feel able to be generous or to treat yourself. e.g. My new bag was a bit expensive but it was pay day and I was feeling flush.

It means you have plenty of money. It can also mean you are felling hot and sticky (clammy) possible even a little unwell.. it is indicated by the skin becoming red and rosy especially on the cheeks of the face. To become flushed can be caused by many things. illness a temperature, nervousness, shyness, embarrassment, fear, fright, exertion. physical exercise and many other causes. This is why you will get many conflicting definitions on the internet forums and from dictionaries. The context is key to its meaning. see the description in the link. https://www.merriam-webster.com/dictionary/flushed. its an American dictionary but it does also give good full and complete definitions for British and other English's

The phrase "feeling flush" means having more money than usual at a particular moment, allowing one to afford things they normally couldn't. It's not exactly slang, but rather informal or colloquial language, often used in casual conversations. The term can be applied to situations where someone has recently come into some money, whether through a paycheck, a bonus, a gift, or any other source of unexpected income, and feels temporarily wealthy or capable of spending more freely. Here's how to use the term "feeling flush" in a sentence: "After getting my tax refund, I'm feeling flush and thinking about treating myself to a nice dinner out." "She was feeling flush this week, so she decided to buy everyone coffee." "Whenever I'm feeling flush, I try to put some money aside for savings instead of spending it all at once." The term conveys a sense of temporary financial comfort, suggesting that the feeling or state of having extra money might not be permanent.

Yes, in the United States "feeling flush" is a common slang term for "having plenty of money." In that context it would be the opposite of "broke." That's what I think it your phrase means. More context would be helpful. "Flushed" can mean red or swollen, but we would use the past participle--"flushed."

Personally, I’ve never heard ‘feeling flush’ to mean having a lot of money but it does appear in American English dictionaries. To convey that meaning I’d say ‘I’m flush with cash’ ‘Flushing’ is used to describe the sensation of having increased blood flow, usually to the face. I think you could ‘feel flush’ if that were occurring. You can also feel ‘flushed with’ I felt flushed with anger when I heard him lie about me.