Here's an example of a bug report that includes a screenshot of a kernel panic:
https://github.com/zfsonlinux/zfs/issues/1433

(In this case, the panic was the result of a bug in a third-party kernel module.)

If you want (I suggest doing this in a virtual machine rather than on bare hardware), you can force a kernel panic by doing, as root:
# echo c > /proc/sysrq-trigger

Here's a complete guide to why this is happening :).

I thought Colonel Panic was this guy.

His commanding officer is General Protection Fault and Major Exception belongs to his unit.

And don`t forget Sargent Unexpected Error.

I read arm instead of ram every time I see the title of this topic...

One pc to the other: What's for supper today?
Other pc: Mutton....again!

Memory going up could be physiological to kernel caching data while downloading.
A certain amount of buffering is expected, to reduce write on discs and reatrict seeking time, while provide a smoothe user experience to the user ( and less disk churn).
Umless you have an extreeeemely slow disc ( like an FDD) and 1 Gb network connection, is very improbable that your Kernel is forced by disc slowness to cache data.
Keep in mind that any modern disc have HW cache too.
This could based on FS type and mount options.

Onother possible cause is a memory leak in the browser you are using to dowbload, or any other program you download with.
A simple way to see if memory growth is normal, and no leak is to blame, is to issue the command "sync", to force the kernel to write buffers on disk.
There are various sync you can issue, to clear various caches.

More invovled options are use valgrind to check Firefox is not leaking memory or explore the "/proc" filesystem, using firefox pid as a start, to check memory usage.

In all cases is a nice way of learning a bit more of how a Linux memory allocation works.