As a child, and all my life really, I've had fears of being underwater. Something about the dark, or being out of control, or monsters maybe.
As an adult, I first ran whitewater seriously in Northern California in 1980. I took a whitewater kayaking course from Western Mountaineering in San Jose. I was no star in the pool sessions, hitting a roll only about 50% of the time. Already being somewhat older (mid 30's) than most other students, and not being a pretty girl, the young male instructors did not gravitate toward me.
Then we went on the Coloma to Lotus run (past Sutter's Mill) on the South Fork of the American River. I was in a Tom Johnson Hollowform River Chaser kayak, and I was amazed to learn the magical moves called ferrying, eddy turns and peel-outs. We practiced these moves in easy water at the top of the run, and I felt very confident. Finally proceeding down river, it all went swimmingly well and fun for me until we hit (old) Old Scary Rapid, then a long class 3. I dumped five times in that rapid, bailing out and having to be rescued four times and successfully rolling up the fifth time.
While hanging upside down in the kayak, holding my breath in a thrashing rapid like a rag in a washing machine, the old underwater fears of darkness, out of control, monsters, and even death overwhelmed me and forced me to bail prematurely. Maybe I could have overcome those fears with further practice, but instead I decided to quit kayaks and try to run California whitewater in the Mad River Royalex Explorer canoe I had recently purchased.
Long story, but I succeeded, and went on to become a pretty good class 4 open canoeist after I moved to the Northeast in 1982. The keys to overcoming fears and becoming confident were formal instruction and every-weekend practice with groups of strong canoeists who were steeped in whitewater rescue training. Eventually, I even became a reasonable roller in C1 and OC1 and, with member here @TomP, even in C2 and OC2.
Here's an article about a wife, Tory, overcoming her childhood whitewater fears via formal instruction:
Blazing Paddles: How My Wife Overcame Her Fear Of Whitewater
What’s the best way to live with a whitewater cowboy? By becoming one too.
paddlingmag.com
"When we got married, I automatically assumed we would go on to be one of those adventurous families who did whitewater river trips. I used to be a whitewater canoeing instructor, so surely I could bring the family onside. There was just the small matter of Tory being deathly afraid of moving water.
"Eventually I learned the source of her trauma was decades old. Tory attended an all-girls camp that only ran flatwater trips. One of the male guides decided to break the rules and take the girls, with zero skills, down a river in their Grumman aluminum canoes. She was terrified. The guides insisted it was all 'no big deal.' Tory came away convinced whitewater paddling was an inherently out-of-control activity pursued by rule-breaking cowboys."