@amygarside,
I imagine it's much like keeping the spark alive in any other aspect of your life (n. b. I am not a nurse), e. g. concentrate on good times, learn new things, look for opportunities to maximize benefits and minimize discomforts and problems.
Of course with nursing you have any number of negatives that can happen any day, e. g. patients die, dealing with a sometimes rude public, relationship with doctors might not go smoothly, etc. Take control of situations as you can, and recognize that sometimes that can mean moving onto another position. Fortunately, there is a demand for nursing, so that's very possible in your field.