Instance unreachable / drops out

Hi,
My instance (i-05a19d44995eb83cd) has, over the past couple of days, become just about unusable. The status check often indicates unreachable but now even when this check passes I still cannot connect to my instance. I use Putty and Virtualmin - both time out/ drop connection. Reboot / restart used to provide a few hours working time but as of today that has stopped working. Afraid I'm a AWS newbie so any help would really be appreciated.
Thanks

Edited by: gedw on Apr 22, 2021 7:42 AM
Not sure if this has any relevance but noticed that Virtualmin dashboard shows virtual memory running at about 97% constantly - even though there is no activity apart from normal services running.

Edited by: gedw on Apr 23, 2021 2:18 AM
As of this morning I cannot connect at all. Reboot / restart has no effect.
Any help - please!