The control module may be at fault, but more likely it is one of the
electronic sensors that has detected an error condition or has failed
completely.  The transmission is programmed to go into "limp mode".  This is
actually 2nd gear (not 1st), and is intended to only be used to get the
vehicle a short distance to get it serviced and save you a tow.  The fact
that it resets itself means the problem is intermittent so will not be easy
to diagnose without the correct computerized tools to query the module and
see why it took that action.

Are there any other symptoms when this happens?  In many cases the
speedometer also fails at this same time and this indicts the output speed
sensor.  When was the transmission fluid and filter last changed?  How many
miles on the vehicle?  Other info might help to determine if a fluid and
filter change might also solve your problem.  If you have recently changed
the fluid/filter and have no other symptoms, then take it to a competent
transmission service place that knows how to service Chrysler transmissions
(make sure they know Chryslers since they are different and REQUIRE special
fluid) or a Chrysler dealer.

Let us know what you find.

 Bob

Don't listen to old wive's tales. Just go to a transmission shop and they
will hook it up to the computer and tell you what the problem is.

The computer that controls your transmission has made that decision, to drop
into 2nd gear. It's designed to do that under a variety of conditions.