Rory, I'm not saying that this is what is going on for you - but one thing I would look at personally is this: when you have the thought, "I don't have the energy" is it really that you lack energy at the moment, or is it just a story you tell yourself to avoid something? Because a lot of times we have been trained (either by ourselves or someone else) to tell ourselves one thing rather than admit something else. If we think it is a failing in some way to be hesitant about meeting some challenge, or if we feel insecure or undeserving to go out and enjoy ourselves, as some examples, it's much more "convenient" to say, "Oh, I'm out of steam, I need a break." I find myself saying I am overwhelmed a lot, but I know a large part of that is really not wanting to look at anything to do with my divorce because it makes me feel like a failure and a reject - so I'd rather be overwhelmed and stressed and go to bed than to feel or admit any of that!
So, what I would look at it I were you is how I feel when I do take that break and give myself time to recharge. While relaxing, do I really do nurturing recharging things, or am I just feeling relieved that I didn't have to go do something I didn't want to do for whatever reason? And of course, with the awareness you find, it's important not be be critical or judgmental of whatever you discover - 'cause it's fine either way. But it just helps to know ourselves better so we don't have to keep telling ourselves fibs.