Need a little advice...driving home from work last night i noticed my temp guage was acting very erraticly.

It is an 02 Civic EX Coupe - 5-speed

I was driving about 35 mph for a good 10 miles then jumped on the interstate. I soon as I was on the interstate, my temp guage shot all the way up to H and stayed there for about 5 secs, then slowly went back down to the middle, or normal running temp. Every couple of miles (driving 60mph through construction zone) it would rise slowly to about 3/4 H and then slowly fall back to normal temp. This did this all the way home (about 25 miles). As i was almost home (driving 25mph through plan), it shot back up to H and slowly dropped down again.

It was completely normal driving to work today and I havent noticed any problems with how it is running. Engine does not seem overly hot and there are no fluids leaking from what i can see.

Any advice on what this may be? Could my thermostat be going bad or possibly the guage/wiring? Also, my check engine light has been on the last few days but i never really pay attention to it because it was contanstly going on and off when i had a high flow cat on there (the exhaust is now back to stock, as is the rest of the car) so i usually just ignore it and it goes away.