I've been having a bunch of symptoms lately that are starting to worry me. I feel like I'm always out of breath, and sometimes I get really dizzy out of nowhere. Fatigue has been a constant partner, and I've even fainted a couple of times, which is super scary. My head feels heavy, and I'm always tired no matter how much I sleep. On top of all that, I can't shake these negative thoughts and just feel so lazy all the time. Does this sound like something I should be concerned about, and what could be causing it?