Welcome,
First, I formatted your pasted code as per directions in the Welcome Topic… which you have read. correct? 
As for your issue, yes… that is “normal” with Ethernet; You would need to physically reset the device to reconnect, possibly a few times as many Ethernet adapters are basically flaky.
You can code in various connection detection and reset routines if you wanted to have the code try to automatically reset and reconnect.
Read up on, and search this site for more information on, connection management and WDT (watchdog timer)