Ragnar.
First of all a fit and a coma are two entirely different things. When a person is fitting they are usually thrashing around in some way. The priority is to stop them injuring themselves by guiding, but not restraining them and ensuring they don't swallow their tongue.
A Coma however is when someone has lapsed into unconciousness and would normally be lying motionless. In that scenario then the priority is to ensure they are breathing and get them into the recovery position, ensuring the airway is not blocked.
In both cases you should summon immediate Medical assistance, an Ambulance.
There are many posts on the Forum which deal with Hypoglycaemia and Hyperglycaemia. They give much information as to how to deal with both types of events. In both instances you would need a blood glucose meter to determine which was happening with certainty. Not something that many people routinely carry around unless you are a Diabetic.
As to a what to do if.......we don't have such a thing here as we just answer questions when asked and offer our advice from experience as a Diabetic. More useful for those that want to know what to do in Medical Emergencies, not specifically coma or a fit the British Red Cross website has some good Video guides and tips for First Aiders. See here:
http://www.redcross.org.uk/standard.asp?id=56899
As an ex Police Officer I know from my own experience that finding somebody in the state you describe warrants an immediate call for an Ambulance whilst carrying out the above First Aid techniques. We never carried any items of equipment other than bandages, plasters and dressings. No meters and suchlike. In any case we were not medically trained other than in basic First Aid. Sufficient to keep people alive and assist in childbirth !
No Police Officer would be able to determine what exactly was wrong with someone so might well assume they were dealing with a drunk, however the Ambulance crew would arrive and usually quickly determine what the problem was and if needed get the Patient off to Hospital. Obviously, we expected the Ambulance Crew to know what to look for. Not something the Police would get involved in.
So the advice to look here is proabaly better directed to the appropriate Red Cross or equivalent website in your own country to educate themselves on the basic First Aid skills.
Hope that helps......
Ken