Connection drops out overnight

We recently switched to a Smarty SIM in our dongle which we currently use for home internet (long story as to why). The connection seems pretty good during the day and evening for working, streaming etc, but in the morning we find that the internet connection has dropped out and we have to restart the dongle and establish connection to the internet again. 

The dongle was originally bought as part of a contract with O2. That contract finished back in April and although the signal was sometimes a bit patchy, it never dropped out completely overnight.

Is this because nothing is using the internet connection overnight, so the SIM/signal is not active?