Is it common for a player to become rusty if he does't play for a long time?

my play probably dropped like 200-300 points easily after i stopped playing seriously

        A dropping off of ability in any activity will occur if it is not engaged in for a significant period.

tiddlywinks?

        Including tiddlywinks.

Don't think of a pink elephant.

As I said, I wasn't that good (maybe around 1700 OTB, 144 in British rating if that means anything to you).  It's more through looking at my old games and comparing them with now; I think I would have given myself a reasonable game within a few weeks but who knows.  Tournaments though are very stressful - only ever played a few of those.  I do think chess knowledge and principles stick pretty well, though once you are into expert play it is probably much more difficult, but I was never that standard.

But I didn't play a serious game between 18 and 53.

I think it's hard to know just looking at games. The strategy sticks with us a long time, I think you're right. The problem is we can't calculate well and miss lots of tactics.

Yes, my tactics were poor when I restarted.  One game early on (I think it was a fried-liver attack or something similar) I was completely steam-rollered in a way that never happened back in the day.  That was demoralising.  But I've sharpened up a bit since, and the Tactics Trainer on here has shown me a lot of stuff I'd never have seen back when I used to play OTB.

The internet is really great for improving at chess; I used to play at most a couple of games a week against reasonable players back then, so progress was slow.

many play at their previous level after a long break, still losing every game

You could take lessons from the backyard professor.

That'd drop another 100 points!

I think blitz is much difficult to play after a long time as compared to standard game.