I fall in and out of love with my spouse about 5 times a year. It can be caused by anything. Too much sex, too little. Not enough communication, or too much. Not enough cuddle time, or too much. When I had an "oven" it was caused by my time of the month. Now it's caused by hormone surges or drops. Depression, messy house, parenting, etc.
Just because you have fallen out of love with your partner, doesn't mean you don't love them at all. It simply means that the special little spark that makes being in love wonderful has taken a vacation. You may experience a period of not being sexually attracted to your spouse. You may feel stuck. You may find that cuddling them feels suffocating. You may feel annoyed with your partner. Everything they do may drive you nuts. Their little nuances that you once found endearing may seem unbearable. Even the sound of their voice may grate on your nerves. This is perfectly (dare I say it,) normal. Give it a bit, sometimes all it takes is 24 hours apart. Sometimes it takes some serious sit down communication, and sometimes all you gotta do is go on a date! Never underestimate the power of a date.
Falling out of love happens to every couple (or household if you are poly) eventually. Don't feel bad, or guilty. It is a natural and healthy stage of a relationship. It happens to every type of relationship; friendship, parent/child, siblings, work relationships. Romantic relationships are no exception. Chances are; with a little work and a little patience, you will be back in love in no time.
NOTE: It can sometimes take up to a couple of months to get that spark back. Don't give up, it really is worth it in the end! If you find that it lasts longer than a month/ month and a half, you may want to seek some couples or individual counselling.