Usually, no need to panic. A little sensor dust is common, and if you don’t see spots in real photos, it’s often not urgent.

Dust is most noticeable in images when shooting at very small apertures, such as f/22. A long exposure by itself doesn’t make dust more visible, and checking the sensor without a lens attached isn’t a reliable way to judge how much it will affect photos. Some specks you notice could even be dead pixels rather than dust.

If you want to deal with possible dust, start with the safest option: use a rocket blower with the camera in its sensor-cleaning/manual-cleaning mode so the shutter/mirror is out of the way. If that doesn’t help and spots begin appearing in photos, you can consider a proper wet-cleaning method or have the camera cleaned professionally.

Bottom line: if it’s not visible in your images, don’t take drastic action yet.