Sweaty Ass
It could be sweaty anything actually. If you are playing something and you are really into it, you will start sweating. On the hands, on the arms, on the armpits, on the legs, hey it is like a real sport after all, we are making a real effort! It can be true, after all if you are casually scrolling on the internet, or playing something to waste time, you will not be excreting bodily fluids. Sweating can also mean nervousness though, a fear of losing. If you start experiencing it frequently maybe it is time to stop playing for a bit.
Weird Tics
When you are in the game, giving it your all, you can start developing those. Worst thing is, you won't even notice them unless you pay extra attention or someone is watching you! Gaming is usually a solitary experience, so you may not even find out until it is too late. I, for example, lick my lips when I am under pressure in front of my computer. Bottom line is, something is not quite right if you are acting strangely while doing what you love.
Eyesight Goes Bad
Once your eyesight starts getting blurry, or you notice you are blinking a lot, maybe it is time for a rest. Or a new pair of glasses. It can usually be detected fairly easily. Do you feel the need to move your face closer to your monitor? Is your posture becoming that of a hunchback? Resting your eyes regularly is the key here. Take breaks each hour, try looking through the window regularly, close your eyes and relax your mind. Of course games don't wait, time flies by and I must play!
Delaying/Underestimating Important Matters
And you are underestimating them because they don't seem so important to you. Once you get addicted to a video game, or video games in general, you start putting them higher on your priority list, sometimes on the highest spot. I know that some people's lives go like this - go to work/school, come back and do some chores, spend the entirety of the evening playing. To them their entire day before sitting in front of their computer is a filler, which they need to go through as quickly as possible. Needless to say this will not give you much success or respect in life.
Lack Of Sleep
The classic example of a video game addict, with a bloodshot eyes and pale face, who sleeps only for several hours. It is not healthy, especially for your eyes, which desperately need the rest. Setting up a schedule and following it might help. Staying awake way after midnight, having fun in the dark and peaceful environment, will only make you lose productivity and feel bad in general the next day. If the games keep you up at night, consider stopping them at a certain hour.
Body Neglect
Fatty smelly gamers are what some cynical people expect to see. And indeed, eating healthy and exercising takes up precious time. You need to prepare your own meals instead of buying a cheap fast food alternative. You need to invest an hour at the gym or outside, doing things you don't really need. After all you are mostly spending your time at home now, who cares what you look like. It makes sense and this is why your mind very easily comes to the same conclusion when you are addicted. A conscious effort is needed to step it up and change your habits.
Social Interactions Noob
Yes, yes, I am going to say something extremely obvious now, but it needs to be said. Gamers, who spend the majority of their time in front of a computer, almost universally suck at face to face conversations. Even if they are good at doing it online. Simply put, the awkwardness can only be beaten through experience and if you are still feeling awkward even when you are older, something is to blame. Maybe you just don't like conversing with people, or maybe a certain thing takes up too much of your time.
Random Bursts Of Anger And Emotion
When you invest so much time into something, it is only natural to become sensitive when it comes to happening within this same something. For example, if you consider yourself very good at a game and lose horribly, sudden bursts of anger, or depression, or anything really, may occur. Another very telltale sign is the blaming game. You blame your poor performance on outside sources, like loud noises, a little mistake your roommate made or..........your teammates. Team games, we love them! Anyway, if you notice you are reacting more emotionally than usual to disappointments, maybe it is time for a break.
Breaking peripherals
The blaming game's next step is breaking your mouse, or keyboard, or even punching right throw your monitor and throwing it through the window. It actually costs you more than lost time and nerves, it costs you good money too and will make you feel bad afterwards guaranteed. On the flipside, it will also make you think next time when you get angry and attempt to pick up your mouse, and smash it. Like touching the red hot oven, it might just teach you to have enough self control to not go overboard.
Hating Your Favorite Games
It is not weird at all to start hating something you used to love when it doesn't live up to your standards. The extend of this hatred varies, but if you feel the immediate need to rant about how this game is bad now, and how its developers suck big time, maybe you should stop and reconsider. Things like this only work if you are a part of the majority, if the problem you found is exclusive to you or a very small part of the community, it is much better to take a deep breath and let it go. You might even come back to the game after a certain amount of time, no need to make a fool of yourself now!