Read through the ping-timeout error section Merlin mentions.
Keep in mind, IRC servers are provided for you to use for free usually at considerable expense to the people supplying the server.
If you are on a network with channel services (where you can 'own' the channel but not have to be there all the time) Then you being idle for hours, without being present really just wastes the bandwidth of the server.
Many servers limit the number of people who can connect, and since IRC means text CHATTING , if you're 'absent' then you're taking up a connection and someone else who would be ACTIVE can't connect.
