High utilisation of memory freezes Ubuntu completely for a long time, with an extremely high access to the hard disk

I observed this occasionally on Ubuntu 16.04 and very frequently on Ubuntu 18.04 (Ubuntu 18.04.1 LTS)

I can reproduce it with a regular use of Chromium, Firefox or LibreOffice, by instance.

In a Ubuntu system, when there is "little" free memory, if I open some new tabs on the browser, the system freezes and it's impossible to do anything.
Also, there are some worksheets that I can open quickly and without problems when I have a lot of free memory, but when I try to open the same document with little free memory, the system freezes.

Then, sometimes the system becomes very very slow but I can change to a tty and enter some commands to kill Chromium, Firefox or LibreOffice... and the system responds again.
Sometimes, after and hour or so the system accept commands again.
Although it's also possible "recover" the system using SysRq memory-full-oom-kill(f), but with the consequence of the crashing of one or more applications (it doesn't have to be the one that apparently caused the problem)

In all cases, the hard disk starts to work intensely... until the system has returned to "normal" condition.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-34-generic 4.15.0-34.37
ProcVersionSignature: Ubuntu 4.15.0-34.37-generic 4.15.18
Uname: Linux 4.15.0-34-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.3
Architecture: amd64
AudioDevicesInUse:
 Cannot stat file /proc/28087/fd/23: Permission denied
                      USER PID ACCESS COMMAND
 /dev/snd/controlC1: carles 1811 F.... pulseaudio
 /dev/snd/controlC0: carles 1811 F.... pulseaudio
Date: Thu Sep 27 15:10:47 2018
HibernationDevice: RESUME=UUID=f06d0abe-a1c3-43f8-8413-9dac4c4a2c8d
InstallationDate: Installed on 2016-03-07 (934 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
IwConfig:
 eno1 no wireless extensions.

 lo no wireless extensions.
MachineType: HP HP ProDesk 600 G2 SFF
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=ca_ES.UTF-8
 SHELL=/bin/bash
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/@/boot/vmlinuz-4.15.0-34-generic root=UUID=31064b95-e0f1-4307-a03e-8cc5b5210093 ro rootflags=subvol=@ quiet splash reboot=pci vt.handoff=1
PulseList:
 Error: command ['pacmd', 'list'] failed with exit code 1: Home directory not accessible: Permission denied
 No PulseAudio daemon running, or not running as session daemon.
RelatedPackageVersions:
 linux-restricted-modules-4.15.0-34-generic N/A
 linux-backports-modules-4.15.0-34-generic N/A
 linux-firmware 1.173.1
RfKill:

SourcePackage: linux
UpgradeStatus: Upgraded to bionic on 2018-09-06 (21 days ago)
dmi.bios.date: 07/17/2018
dmi.bios.vendor: HP
dmi.bios.version: N02 Ver. 02.36
dmi.board.name: 805D
dmi.board.vendor: HP
dmi.board.version: KBC Version 05.36
dmi.chassis.asset.tag: CZC60572P2
dmi.chassis.type: 4
dmi.chassis.vendor: HP
dmi.modalias: dmi:bvnHP:bvrN02Ver.02.36:bd07/17/2018:svnHP:pnHPProDesk600G2SFF:pvr:rvnHP:rn805D:rvrKBCVersion05.36:cvnHP:ct4:cvr:
dmi.product.family: 103C_53307F G=D
dmi.product.name: HP ProDesk 600 G2 SFF
dmi.sys.vendor: HP