Sometimes that can occur when a guitar has been moved from one environment to another with wildly varying humidity levels and/or seasonal changes. It can be quite noticeable and in extreme cases can cause the fretboard to dry out enough that it shrinks and the frets stick out and can cut your fingers with the sharp edges for example. In very dry environments it can be best to keep the guitar stored in a hard shell case with a guitar case humidifier, and ensure the humidifier is wet from time to time. Dunno if your problem is humidity related but it's worth consideration.

HTH

Ziggy does, and Weird and Gilly.

In addition to the humidity, it probably needs a truss rod adjustment, however I recommend having this done at a shop. If it goes out often though it can be worth it to learn how to make the adjustment yourself too, there are lots of videos on youtube etc. that show how to do it, but you need to be very cautious as misadjustment can potentially cause permanent damage. Having said that, I don't know of anyone who has ever damaged one either. :)