Mills will attempt to claim 49erFX gold in Japan after winning the 470 class with Saskia Clark in Rio last year.
After suffering concussion in January, Mills this week had to pull out of her debut 49erFX regatta with stomach problems.
"It has been frustrating but life is like that," said Mills.
The Dinas Powys sailor had to withdraw from the Trofeo Princesa Sofía event in Palma where she was competing in a mixed boat with Alain Sign.
"I have to take it on the chin and be as relaxed as you can," Mills told BBC Wales Sport.
"I feel lucky it's the right time at the start of the Olympics cycle and not the end and both my medical issues have not been more serious.
"You notice the weeks you miss when you are this stage of the learning curve.  It is a new skill and there is a lot to learn.
"I have a lot to catch up on. I did a week in January before I got my concussion and then did three weeks before my stomach problem. So I have only had a month in the new boat."
Mills, 29, was forced to have a gastroscopy and has been told to rest for at least the next 10 days before returning to the water.
"I found out I was lactose intolerant about a year ago so I changed my diet accordingly," explained Mills.
"In the last month, I started getting bad cramps and constant stomach pain.
"It got so bad I had to fly back from Palma last week and get it checked out in hospital. It was quite gruesome. Luckily I was sedated otherwise I would have freaked out."
Mills remains determined to try and make history in Japan in just over three years' time.
"The chance to compete in Tokyo and win another gold, which would make me the most successful British Olympic female sailor of all time, would be awesome," said Mills.
"Ever since I was a little girl and started sailing since I was eight and met Ben Ainslie at an event, I fell in love with the sport.
"It was always my dream to be the most successful British Olympic female sailor of all time. I don't take my eyes off the end goal."
Olympic gold medal sailor Hannah Mills has revealed her frustration at another setback in her bid for more glory at Tokyo 2020.