There are a couple of directions you can take here, any version of the below is cool with me as long as you don't have any resentment in your answer.

I have been at this company for 3, 5, 15 years and am looking for a change. I like the company a lot, and I like my manager, but I have gotten to the top of my discipline there and the company / department is of the size that I am not learning any more. This is a company that specializes in "your discipline here" or is larger so there would be more opportunity to grow my skill set.

The company just had a lay off and I am still employed and am confident that they will have another lay off within 3 months, so I just want to see what other options are out there. I am talking with my manager to see if there is anything I can do to expand my skill set and make myself more valuable to the company, but even my manager is suggesting that we all look for new jobs.

I was just laid off from my company and took a break for the last few months. I figured I wouldn't have a chance to take a long break till I retire so I made it a conscious decision to spend more time with my family, remodel the kitchen, learn a new skill set, do something you always wanted to do and have a passion for.