Unfortunately this room is under a flat room, south-south west facing semi detached so it gets sun from sun up on the side and top and top and back most of the day into the evening with poor airflow and the damn hot water tank as well. Its awful but the only room that works. WIthout aircon its horrible, I've made do with a portable POS aircon in the room. For years I've sat next to a ridiculously loud aircon, I'd kill to get them to install an external one which would be more efficient, stupidly quieter and just better all around.
Its not necessarily the heat, when you've got a room inside with a person in it and very little airflow the room gets sickeningly stuffy. I can only have the aircon on for 5 minutes at a time and it just removes SO much moisture its fantastic. 35C with no real humidity is easier to be comfortable in than 20-25c with high humidity. Outside I love the heat, had no problem walking around in 40-45C in a hot summer in Barcelona, but inside in a room with no airflow sitting all day, its killer. It saps all your energy, kills your concentration, AC is well worth the cost. They also aren't particularly expensive to run because they are only at full power for a very short amount of time overall and its a heat pump, they are pretty damn efficient, you aren't creating heat, or cooling it, you're just moving the heat.
For me its a necessity because I suffer from migraines, the summer humidity/heat/weather in general can screw me up badly. I had a headache for the past three days with the AC, just less severe and far less frequent, pre-AC I'd have summers where I'd have 4-5 migraines a week for 2 months of the year.