When you are declaring your condition, you may be asked about unplanned hospital admissions in the follow-up questions. A trip to A&E is only classed as a hospital admission if you are admitted to hospital as a result of that visit to A&E.
If you are well enough to go home after your visit to A&E, this would not be classed as an unplanned hospital admission. You would still be required to declare the condition that required the trip to A&E.