Try and plan for it as much as possible!
I decided to go back to uni to do a Master's two years ago, as this was the only realistic way I could change direction (in the way I wanted to). It helps having an understanding OH … we did a lot of saving up the year before I quit my job, then down to one salary for a year. It was tough financially, but we managed and actually ended the year with more money in the bank than at the beginning (= better spending habits!).
It's the best thing I ever did and I have no regrets – I earn half what I earned before, but the improvement in quality of life is incredible and my prospects for better paid employment in the future look positive.
Good luck!