Why is my car overheating? Thermostat?

It's a 1996 Honda Civic. 126,000 miles. I've been gone for like 6 months for college. So it did a lot of sitting. But when I came back, it drove fine. But suddenly I noticed the heat needle raising all the way to red, but I couldn't park because I live in a city setting and couldn't find parking, but after a few minutes, the heat needle went back to normal. It was weird. It over heated and unheated while driving. It does this a more often than not now. Could it be the thermostat? I'd love to fix the problem. Thank you

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