Ubuntu started to slow down, what's the matter?

Question

linux

Hello. Installed Ubuntu 14.04. Works for about 6-8 months. Last month there are brakes. And they do not always appear, not every day. Always open Chrome (10-20 tabs), Sublime, started the server from the command line gulp or bem enb, Slack. If it starts to slow down, then even if everything is closed, the brakes will remain. What can be tested at the time of the brakes? What do you advise?
Laptop:
i5, 2.ghz
6GB DDR5

Answer 1

Here's how it starts to slow down, then you are welcome with the output of
top
free
df -h
iotop

Answer 2

Maybe swap?
increase in /etc/sysctl.conf
vm.swappiness = 10
to swap only if the memory is occupied by 90%
Well, check the disk, maybe it writes something somewhere ..

Answer 3

Is it ok after a reboot?
It was exactly as you describe, it turned out to be an HDD.
Look in the system log.
less /var/log/syslog
or
grep -i 'fail' /var/log/syslog | less
grep -i 'error' /var/log/syslog | less