This isn’t specifically about running and cycling..but I wasn’t sure where to post this…

I like to go to the gym and use the elliptical, usually for 2-3 hours at a time. I usually don’t try very hard and just go at a steady pace, before working out I have tons of energy (I drink a lot of caffeine). My muscles never get sore but when I get home I feel dizzy and mentally tired. This is bad because I often try to do homework after the gym but it’s impossible to focus or think straight..also sometimes when I move my arms a certain way my fingers get tingly which is really weird, and my head feels really heavy. It’s not like I’m sleepy either

How do I get up my mental energy after a workout? I always feel dizzy and the thought of food makes me nauseous. I was thinking it might just be a caffeine crash, and I’ve been trying to drink less coffee during the day..

overall I just feel unmotivated and spaced out. does this happen to anyone else?

I would say the first step would be NOT to use the elliptical for “2-3 hours at a time”!!! WHAT would possess you to *want* to do that and what benefit do you think you are gaining from it????

Symptoms suggest dehydration. Consider that on a simple 42 minute mile run my little logging app says I burn between 0.75 and 1 litres of water. 2-3 hours on elliptical will need a lot of water going in, before during and after. I drink 3+ litres a day to avoid dehydration making me useless mid afternoon, it almost works, but epilepsy meds counter it.

First time I have had cause to disagree with basket lady here. I used to run marathons and knew many people who would use low intensity long jogs as a way to exercise because they enjoyed the low intensity activities that made it easy for them to take a mental absence. There are gains to be made from this but in truth only the ability to keep doing the same thing consistently for a duration, I would always recommend variety. Even when I did stupid distance running I mixed things up to keep it interesting and ensure I improved overall, back then it was predominantly intervals etc. now there are plenty of studies showing resistance training etc. is a good accompaniment.
The repetitive of your activity is not great for performance or aesthetic goals but if it is all you enjoy it beats nothing every time. Still intrigued as to why you choose that activity alone though.

dehydration, yes and I don’t think “tons of caffeine” is helping either…try eating right for energy and not using caffeine

I drink a lot of caffeine, but I also drink more water than the average person does so dehydration isn’t a problem for me. Crazyoldman I wish I could run a marathon! I used to run for hours everyday but forced myself to stop because I was having serious knee and hip problems.. The sad part is I’m only 24! When I can I run on the treadmill for 10-30 minutes at a time, but I still have to be careful about injuring myself.

I guess I am kind of insane but it’s nice to shut my brain off during the day.

mixing it up would probably help, I’m just not used to doing resistance training or any of the machines so it’s kind of intimidating.

More water than average could still be too little with that level of activity. It would be worth looking into it. Dehydration is something the human animal suffers with easily.
The other issue could be that you are getting such a mentally relaxed and physically drained state your body is just wanting sleep or further relaxation.
The most common issues regarding running is definitely bad technique, especially for knees and hips. I weigh in at 1.5 times my running weight and at 40 can still run with virtually no issues with my joints, knees and hips have both been damaged outside of running.
It’s quite hard to use resistance machines badly, they are designed to be safe for the least knowledgeable. If starting on free weights watch a lot of videos and get friendly with gym mirrors, they are your best friend if training alone and avoiding injury. Best option is to find someone to assist you in learning the moves like a good PT, but be sure they know their stuff first. Some PTs know aerobic training etc. incredibly people don’t realise that being able to run, cycle and do basic bodyweight circuits doesn’t make you ideal to demonstrate resistance movements. Don’t be intimidated by a bigger PT the chances are they will have been plying with iron longer and will be able to show you best form.
You are evidently wanting to train and stay safe, a good standpoint. Think about what you want and then come back to find out what will give that to you best. If you want more energy you need to do higher intensity stuff, the irony that to have more energy you need to use more.