OERR: ORA 603 "ORACLE server session terminated by fatal error"

Error: ORA 603
Text: ORACLE server session terminated by fatal error
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Cause: An ORACLE server session is in an unrecoverable state.
Action: Login to ORACLE again so a new server session will be created

*** Important: The notes below are for experienced users - See Note:22080.1

Explanation:
A severe error occurred so this session died.
This is a fairly generic error that can be raised in many places
so the error itself is of little use.

Diagnosis:
See the server side trace file and alert log. There is usually another
error on the error stack to show why the session died.
Eg: ORA 1092 - Instance terminated.
The stack trace should show what we were doing when we died but this is
often a side effect of some other session dying .