"So what exactly do you do then about the feeling? One isn't always practicing mindful meditation 24/7. So what are you doing in the times where you aren't? Aka what is the "real life" application (not sure if I am saying this right)."
Thanks for bringing this up socrilus.
There are two practical components of mindfulness - concentrated meditations, maybe 2-3 sessions of 10-15 minutes a day, and then also as you progress with the concentrated sessions, begin to expand your mindfulness meditation out into the rest of your day, which is very important. It can be hard to expand it out to the rest of your day at first but as you gain practice with the concentrated sessions it will become easier and will eventually become habit. The first place to start would be to, at the end of a mindfulness session, start going about your day and see how long you can carry the mindfulness with you, and then try to catch yourself throughout the day when you are having negative thoughts or are lost in thought.
So mindfulness might actually play out like this: You're going about your day when you have a "Man I feel horrible" genre thought, then that single thought might generate more thoughts and before you know it you're lost in thought, or are at least distracted. The idea with mindfulness is that you begin to catch yourself earlier and earlier, before you're lost in thought. After a long time of practicing you might catch yourself at "Man I feel-" or even earlier.
But the important thing to understand is that as you practice mindfulness, your biology changes so that you will sustain the mindfulness mindset easier and easier. You won't have to exert the same level of concentration to be on guard against these thoughts or being lost in thought in the endgame of mindfulness, it will just be habitual and you won't have to think about it very much. Your biology will also change so that you have less of these thoughts in the first place.
"The only difference I see is that you can stop thinking about the consequences but objectively they still exist whether you obsess over them or not."
Lets focus on that last bit - I think its important to understand that mindfulness can actually change biology to improve quality of life by decreasing the consequences (directly starting to reverse the consequences of MDMA/LTC related biology).
"Basically, how exactly can you stop worrying about the future when its the problems/symptoms in the present that are causing you to worry about the future. It seems really difficult unless you get rid of the symptoms."
Another good point to bring up - the answer is that the goal with mindfulness is to catch the "worry" thoughts as soon as they begin and let them flutter out, don't get caught up obsessing over these ruminating thoughts and let that worry thought stepping-stone into another worry/depressive thought, and return your attention to your breath/thoughtlessness before an hour of lost in thought rumination gets started.
If you can practice mindfulness enough, you'll become constantly vigilant, constantly with your attention on the breath except for when doing a task, and then very few of the depressive/worry thoughts will get started, and this will improve biology. Even if you're not having crystal clear "I feel horrible" voice-in-the-head thoughts, focusing your attention on the breath will help as well.
I hope that this answered some questions, as always feel free to ask anything. In summary, mindfulness isn't just good for ignoring the thoughts that are caused by the symptoms - sometimes the predisposition to these thoughts is not just caused by the symptoms that you feel (like HPPD visuals) but the biology itself is causing more worry/depressive thoughts (in other words, some other people could feel a very similar way but their brains wouldn't be as predisposed to rumination), and consciously directing energy away from the worry/depressive thoughts circuits will allow them to weaken and atrophy, and there are other neural changes that will result in better quality of life as well.