Flight of ideas can be a symptom of either a manic or a hypomanic episode, as well as other mental disorders. The name sounds like it's something experienced in thoughts, but it actually has to do with speaking rapidly and jumping from one topic to another.
I had a friend with bipolar I disorder who displayed classic flight of ideas in her speech. She'd talk nonstop and would, for example, go from talking about her new dishwasher to when she bought her china to a cute little store she visited years ago to her ex-husband's illness at the time to why she couldn't mow her own lawn. I could see the places where one thing reminded her of another, but it happened so fast I really had to pay attention - which was hard to do, especially if I was depressed.
I could barely get a word in edgewise. If I made a comment, she'd ignore it; if I asked a question, I'd just set her off on an entirely new series of tangents. Flight of ideas can be disorganized or extremely difficult to understand when it's severe. My friend's speech wasn't that bad - it always made sense, but oh, how tiresome and even obnoxious it became after a very short time