I've always been a heavy sleeper, and more recently I'm also tired a lot of the time too.
Has anyone here successfully overcome a sluggish metabolism, and increased their energy levels through lifestyle changes?
What did you do?

Yes!!! Just 3 months ago, you couldn't pay me to move at all! I had zero energy, I stayed tired and drained for no reason. After eating I would pass out fall sleep due to feeling super drained. Just walking to the door would exhaust me so bad! But a lot changed when I started working just 3 months ago! Once I started moving more, becoming physically active, my entire life changed and is still changing! My energy levels have increased so so so so much. My stamina and endurance have increased tremendously! Now, I'm to the point that I can't stand not to move lol. My metabolism has started back working with my body. I'm down from 225.6 to 209.4. I still have a lot of work to do as far as losing weight and becoming completely physically fit but I'm grateful I'm not where I started anymore!

if you miss breakfast you are shooting yourself in the foot most cereals are full of 20p for the swearbox. get some porridge or muesli down ya. if you want to put on weight and train weights or any kind of training and get something out of it your diet needs improving. you are best eating small meals little and often, every few hours. you will get more energy by eating well. if you want to put lean muscle on take your weight in kg, double it and thats the figure in grams of protein you need to eat through the day to maintain muscle mass. times this by 3/4 for you good carb intake. get some bleedin fruit down ya too.

Yes!! Get your hormones/thyroid levels checked, nutrient levels as well (vitamin D, b12 etc etc) good place to start.

For me...a plant based diet, proper supplements got me going (I was super low on vitamin D and b12). I started walking a few minutes per day at 265 pounds and now I am nearing 220 pounds and I walk 45 min-60 minutes per day. I have so much energy!