I'm 18 (girl). I lost almost 20kg over a period of 3 months..
And I just want to know if I lost the weight healthily.

I looked at my family members, they are all slim.
For some strange reason, I was borderline obese. Odd one out.
I eat the same home-cooked food as them. Every morning, afternoon and night.
I never eat out.
I never drink soft drinks (unless forced to on a special occasion or something).
My sisters drink alcohol; eat out a lot, and drink more juice than water. And never gain a pound. (I'm not the same. I don't consume any of that stuff and yet I'm the one gaining the weight.. not them.)
I don't drink alcohol. Ever.
I am as active as my sisters and parents. Which actually.. probably isn't all that active. I'm not a lazy slob couch potato or anything. I move around and stuff. I just don't engage in sport. (Not very co-ordinated).
I work 40hrs a week. My job is quite physically demanding..

In these last three months..
I did not increase my physical activity at all.
I lost the weight purely on diet.
Basically, I ate exactly the same food as I would normally eat.. only I ate smaller portions and 1 serving (instead of a million).
I also drank a lot of green tea (I just like green tea..) and kept hydrated.
I also reduced the amount of carbs (bread, rice and pasta) I ate; and ate more protein. (So, low carb-high protein). Like, let's say my mum has made a chicken curry for dinner with rice and veggies. The ratio of rice to chicken is significant. There is only a blob of rice and a heap of chicken and a heap of veggies on my plate.
And after I made these SMALL changes to my diet, the weight just FELL off me.

Am I okay?
I feel really good.
I'm a lot less tired. My concentration is better. My self esteem is better. My skin is MUCH better.

I'm just wondering, are my results extreme?

I'm just worried because I lost a lot of weight without ever having to run or exercise with intensity.

So you ate considerably less than you had been eating, ate considerably fewer empty carbs, created a caloric deficit, and you lost weight.

Sounds pretty normal to me.

Losing weight is probably 90-95% diet; there's a common assumption that if you're not exercising like they do on The Biggest Loser, that you can't lose weight. That's not true at all and that idea really does people a disservice.

Those really aren't small changes, though. Cutting calories is how you lose weight, and that's what you did, plus you cut carbs -- pretty big changes actually. Are your results dramatic? Yes. Are they healthy? I have no idea! It's impossible to say based off of a post.

Exercise isn't needed to lose weight, so your results aren't atypical at all. Diet is basically the only thing that HAS to be changed in order to lose weight, exercise is just a bonus, and of course great for fitness and overall health.

Depends on your starting weight too (and body composition).

Plus, you're 18. It was easy for me to lose at 19 (I know it's hard for some, but for many teens, it's an advantage). I had to lose again at 30 post-kids, it was so much harder.

It doesn't have to be torture. Congrats!

Your results sound extreme, but relatively normal. It seems like your way you're going about things is good. Cutting back on calories with smaller portions, eating less carbs, and possibly drinking green tea are all helping you. As long as you're not feeling hungry, weak, fatigued, or any other negative effects, I would say that you're fine. If you are still worried, talking to your doctor would be a good idea. My only suggestion is to take a daily multi-vitamin just to be sure that you're getting the nutrients you need.

Honestly, you don't need to exercise to lose weight. You lose weight by creating a calorie deficient. Exercise will tone your body and may help with skin elasticity. It is not required for weight loss though.