Hi, I'd like to help you with your question.
It is very hard to be motivated to go to a job you don't like. That is true with anything in life that you dislike or feel an aversion to, such as chores at home or going to the doctor's.
Although the rewards of your job are great, you still may want to consider other options. Your seniority is wonderful but the experience you have could also get you a very good position somewhere else where you are more happy with your job. It would not hurt for you to take a look at other opportunities just to see what is out there.
However, if you feel it is important to stay where you are, then there are some things you can try.
1. Vent about your job- just don't do it at work. But at home, let out your feelings. Talk to friends (who don't work with you) and family who are supportive.
2. Prepare an escape plan- it doesn't mean you have to do it. But be ready in case you begin to feel it is not worth it anymore, even with good benefits and seniority. Re do your resume, post a profile on LinkedIn, start networking, etc. It will make you feel productive and give you a quick way to escape your job, if it comes to that.
3. Plan time off more frequently- you only have a limit to how much time you get for vacations, but plan it out so you feel like you are at work less. Instead of taking a week at a time, make your days off into several long weekends. Then when you do have to go to work, it makes it easier to get through a shortened week rather than a Monday-Friday week.
4. Change your job- I don't mean get a new one. But try to make changes to your current job so you have more choices and do more you enjoy. If you have any control over your job, add duties which interest you more. Or change how you do a task so it is more fun.
5. Develop better co worker relationships- there are some jobs that are bad just because of the work. But when you have great co workers, they can make any job easier. If you already know everyone in your department, try getting to know someone in another department. Or try going out with co workers to develop better working relationships.
6. Give yourself a break during the day- at lunch go out instead of staying in. Do a little shopping or treat yourself to a nice lunch once a week. Even just a short walk sometimes helps refresh you enough to tackle your afternoon.
7. Try to look at your job with humor- laugh about stupid stuff you have to do. Post comics that make you laugh around your desk or work area. Watch a short comedy skit on your computer at lunch time. Laughter helps promote good hormones and makes you able to face things easier.
Remember, what ever you go through with your job, keep in mind that this too shall pass. Your job will not last forever. Someday you will retire. Just thinking about what you will do once you do retire can give you hours of imaginative fun while you work!
Let me know if I can help in any other way,