samsung galaxy s4 pressure sorry if this is slightly off topic but please could you give your thoughts to this

recently,  I had my s4 in my front pocket and while sitting down in a chair i could feel that I was slightly sitting on the phone

it had a back hardshell case and it was the screen facing down in the pocket

when I took it out everything was fine, can't see any scratches/ cracks

my worry is that because there was some pressure put on it, could there be some damage not visible now that could cause some problems in the future? should I be worried?
No , you don't need to worry at all. As mentioned if there are no scratches/ cracks on your device it proves how tough these devices are in reality. 

Here is an example which shows how much of actual force is required to damage any device. Taking the case of a pencil: 



Think about how tough your device is ? Galaxy S4 can handle pressure of more than 130 lbs whereas this pencil was just at 80 lbs.

So, no worries your device should be absolutely fine. In this case you also had extra protection with additional hardshell case to it.