Desire is never truly “spontaneous” or “out of nowhere”. It seems intuitive that there would be a trigger, whether it’s explicit visual sexual stimuli, a memory, or a moment of emotional intimacy with one’s partner.
Some of us have a hair trigger. Some of us have a long fuse. Both are okay and they can change over time.
The most important factor is having a partner you are truly sexually attracted to, and that’s not “spontaneous” either. Being lustful toward your partner 24/7 is an incredible feeling, but that attraction has to be maintained to keep desire heightened.
Some people never feel that level of desire. Individual sex drive is as variable as people themselves. What’s important is doing what works for you and your partner and keeping the lines of communication open so that each person’s sexual needs are being addressed. If you used to have a hair trigger and now couldn’t care less if they ever touch you again, there is some investigating to be done. Stay curious. Work together.
Sex is awesome.