Iknowall558, how brave of you to open up like this, revealing feelings that, as you say, many of us might hesitate to acknowledge in public! You are all the more to be respected for voicing them though.
Is it normal? you ask. In my opinion, it's definitely nothing to be ashamed of, but there's no reason why you should put up with those uncomfortable ups and downs that make you suffer emotionally. I agree with the other posters that you should seek help from an expert. More and more people do it nowadays and sometimes it works wonders. I'd give it a try, it may help you tremendously and permit you to remain in that state of "contentment" for much longer periods of time and the lows to be shorter and less intense (mind you, we all have our mood swings, so you'll never be totally rid of those emotional changes). I'd just make sure the help you get is not only professionally competent, but also compatible with your personality.
All the best to you.