If you are supposed to let go of your thoughts, desires, etc then what exactly is the point of doing anything in the first place?
Rational conscious thought is very important and we wouldn't want that to vanish completely by any means, but I wouldn't want someone to constantly be at the mercy of their thoughts if their thoughts are frequently negative and ruminating. I think the goal is to strike a balance between reducing negative rumination/anxiety/lost in thought and maintaining intact conscious decision making. This probably involves learning mindfulness with a couple concentrated sessions of mindfulness a day, and then learning to apply it throughout the day when having conscious thought isn't important to attaining goals, or that rather not having conscious thought will help you more with a goal of say, achieving mental health (in the long run).
I am not able to rationalize this and its one of the scary thoughts I get when I do it. Also, if you aren't supposed to think about getting better then isn't this itself an inherent contradiction in that for mental healh stuff people say go get help etc but then the "help" is this mindfulness therapy which seems to have the opposite message of "not changing". I feel like all this stuff and thinking about it is just delaying my recovery and if that is the case maybe I am better off just with other things?
If you don't feel like mindfulness is good for your mental health then by all means try the other routes like cardio and cognitive behavioral therapy, and of course it would be great to talk to a psychologist about this, but just to put my two cents in about the goal of mindfulness and what that means for an LTC; The ultimate goal of mindfulness really is to just stay in the present. Not regretting the past, or worrying about the future. Just simply paying attention to the present moment. The present moment could be bad - you could be in emotional pain, but the goal is to not have too many thoughts about the pain. The idea here is that if you practice mindfulness enough and become proficient at it, and very importantly the physiological changes come along with that, then the present moment will become better.
So you're changing your thought patterns and your biology, but it does take some time. And having almost existential crisis type thoughts interrupting you during/after the meditation is really the opposite of mindfulness, so I wouldn't call that successful mindfulness I suppose. If those thoughts are bothering you, its ironic that mindfulness is really supposed to quell those sorts of thoughts if done successfully.
I think there are times for cognitive thought and times for the brain to relax and try to just stay in the present moment. As far as being able to let your mind go blank but still retaining your typical life goals/desires and that sort of stuff, bedtime is a very good example. Letting your mind go blank during bedtime to let yourself get some rest is absolutely conducive to achieving life goals etc, because you need your batteries fully charged to go about your day at 100%. Yet some people find themselves awake until 3am ruminating, lost in thought, thinking about this scenario or that scenario, this memory or that conversation they had 5 days ago. Being lost in thought at 3am when they could've been sleeping had they been proficient at mindfulness (and had their brain adapted physiologically to the mindfulness practiced over the seasons) is a perfect example of when its a good idea to let go of thoughts and desires, not because you want to let go of those thoughts and desires
indefinitely, but rather that you will be more capable of attaining those goals (attaining mental health for example) if you can let go of the thoughts when they are not actually helping you.
So I guess I wouldn't say that mindfulness is about "not changing", as much as it is learning to stay in the present moment when your theorycrafting/problem solving mind doesn't need to be kicked on. Over-analyzing can give people a lot of grief when it comes to LTCs, but more regular mental issues as well. I think its very frequently the people who over-analyze that get LTCs (at least some of the people I've asked have claimed to have issues with constantly thinking before their LTC).
I hope this was helpful. Feel free to ask any questions, and as always do whatever you think is right for you. If your mind is pushing back against you when you try to do mindfulness, that might be a sign of needing to practice it more if its not too mentally destabilizing. I would consider it akin to becoming sore after working out.