In addition to the other informationa already raised, for the person asking about equipment onboard...
Emirates also have a monitoring device onboard called a Tempus, basically it will give the CC all relevant information like heart rate, blood oxygen, temperature, etc etc AND this can be relayed to Medlink and appear on a screen in front of them so they can see exactly what is going on with a patient. It has the ability to send video and/or photo so you could take pictures of any injury or what is going on to allow them to better analyse the situation.
Apparently it has saved them millions in unnecessary diversions for suspected heart attacks which were other things. Basically, it takes the "guesswork" out of it and assists them to make the decision to divert or not based on the information gained from the unit. (It is portable and can be used in the cabin without the need for cables, also uses the phone system so they can patch in the dr, the captain etc...) very good system in my opinion, have seen it in use.
Along with this you also obviously have the defibrillator and the medical kit, which has everything needed including the same cardiac medication trays & IV equipment used in hospital. These are meant for qualified professionals only (decided by Medlink of course) who then provide coverage for the professional and the crew should anyone decide to sue later on. If necessary crew can give certain medications ONLY if advised by the Medlink doctors - who are trauma/specialists surgeons etc- but they have to follow instructions exactly and be willing to do it, to be covered.
In many cases, you would probably have more chance of surviving onboard than you would at your lovely yet remote holiday destination!!!!
With regard to medical conditions, it is always best to check with the airline (most large ones have their own doctors/medical departments) as your GP might not be fully aware of possible complications due to air travel. Airline doctors know all of the potential issues that may arise and have seen from their experience so they are probably better equipped to make a final decision on whether you should travel or not. Also, some people get the letter a long time before they travel and anything can happen just prior to the flight. Better to get offloaded and be a few flights behind than to have a diversion right??
Hope this helps to reassure you that you really are looked after on board