I had sleep apnea and now don't, so I can give some background.
Since you mentioned getting testing equip, it sounds like you won't be doing a sleep study but instead will have the takehome equip like I had. The equip will monitor how many "apneas" you have per hour, i.e. stoppage of breath. 15 per hour or higher is diagnosed sleep apnea, 5-15 will depend on their analysis, and under 5 is not sleep apnea.
I had 48 per hour. Sounded high and probably was, but they said the highest they tested was 112 per hour! Anyways, I was a walrus at the time which is probably why it had developed into how bad it was - 6'1" 280 lbs.
It however wasn't really the cause. I was having wisdom teeth taken out around the time I got diagnosed and my surgeon for that happened to be an expert on sleep apnea. He took one 2 second look in my mouth and said "your tonsils are huge". I had asked him because I wasn't satisfied with the thought of being hooked up with a loud mask for a 1/3 of the rest of my life, and was glad I asked!
So - went through the procedures of my HMO to confirm and wound up getting a
UPPP surgery or something pretty similar to it. The pain after the surgery was pretty bad for a few days (eating ice was the only thing that helped at all, even with pain killers, and could only sleep for a couple hours at a time before the pain woke me). After that though, it wasn't that bad to deal with, and a few weeks later, back to normal. Didn't cost me that much in deductible and I don't need a loud mask every time I sleep.
Now - you might expect afterwards that holy shit, sleep would feel like the best thing in the world, right? It wasn't THAT noticeable of an immediate improvement...over time I'm sure it's helped, and more importantly I'm no longer a walrus (195-200 lbs now). So while sleep apnea may be robbing you of energy, it may not be the only thing.