I mentioned my Anxiety (diagnosed) on the one I have just done for a new role, was completely honest about everything. Ironically they called me up and asked me questions about hay fever and weren't remotely interested in my anxiety
Its worth remembering that they can request access to your medical records if they need to so anything you neglect to mention that they might then see if they request them is never a good thing. You need to remember that the OH form is there so that they can deal with any adjustments they need to make to help you.