Why are psychedelics so fucking scary? I've only ever had horrible experiences on mushrooms...

My take is that you're afraid of your own thoughts. I used to get super paranoid on weed and psychedelic shit like mushrooms alike. Eventually I got sick of it and I decided to just full on accept it, to think through it and accept whatever thought I was having, inhale some rough thoughts as is when I'm not in drugs so it made more intense. It got a lot better for me after that and actually ended up calming me when I get high now, probably because I delt with thoughts that I would usually bottle up or brush aside if i wasn't high.

I feel you OP. Its also a lot to do with age. When your brain fully develops at 25 most people can't enjoy weed or other psychs the way they use to when they were younger. I still toke regularly but I certainly perceive my o anxious thoughts and thoughts in general a lot more nowadays. Certainly as others have suggested, headspace going in is a big factor as well.

Very true too. Some of the greatest utility I get from toking is the fact I can quickly identify what has truly been making anxious or thinking a certain way.

Age... it's about perception

How does one actually find out? I can’t even figure it out sober

To some extent but your brain physically and chemically changes at around this age. Basic physiology.

It becomes far more obvious because all of your feelings are amplified. So when you get high and lose control over your ability to regulate your thoughts it becomes much clearer what is troubling you, something you might of tried to push to the back of your mind when sober.

Psychedelics reflect your mental state user. Your nightmares aren't because of the drugs, the drugs bring them out. It's your job as a psychonaut to confront your demons.

I use LSD every other month or so and for the first five trips I kept sobbing uncontrollably because I kept getting stuck on my dogs mortality. I never think about this otherwise and I'm a lot more comfortable with it. I dont look at it as a clock running out, but as more time with my favorite creatures on Earth.

Confront your demons and kill them, user.

How does one not give a fuck? I want to try the ol marijuana again but did too much last time and had a panic attack. How does one learn not to give a fuck and just accept what is coming??

You're a pussy.