This is an interesting question ---
I find being a human on the planet entails happy and sad days no matter the career. Working with clients when they are having difficult times or when they are having wonderful times doesn't affect me now like it used to. I find becoming stable in myself allows me to be grounded when working with others in that their stories don't rock me. I use energy as well as psychology when working with clients, so I do cleansing rituals before and after a session. This has helped me remain within my business, and my boundaries and my emotions. I meditate and exercise regularly and eat healthy - no gluten and choose organic foods. I drink lots of water and stay away from alcohol for the most part. Taking care of my mind and my body helps keep my energy and emotions balanced, too. These things have helped me, and I hope they will help you. I also use art for healing with clients and on myself, as well as writing in a journal. I am constantly learning from my clients and keeping my balance helps me remain stable in my emotions. This does not mean I do not feel. Feeling my emotions is a key part of healthy living. I feel deeply, but other's lives do not pull or push me in and out of emotions.
In being in the field of HR, I am looking at this question through a different lens. The short answer is "yes". There are some days that I feel emotionally drained, due to the nature of the conversations I have had with associates during the day, and hearing their stories. Being a human being, you feel empathy and I always try to put myself in their shoes.
That being said, you also need to find a balance and a way to de-stress, so the feelings do not bog you down to the point of having a negative effect on your own emotional well being. I always have to start the day with exercise, as it gets my endorphins going and I have a greater sense of peace and the ability to think things through, without having a negative impact on myself!
Everyone has happy and sad days! Maybe the same thing affects your mood more on one day and less on the other, maybe it's the hormones, maybe there are some external factors ( like the weather). You cannot predict what's gonna happen. But you can make sure that your mood lightens up by things you love!
Exhausted from work? take a break, do some exercise, or watch a show.
Relationship problems? distract yourself with your favorite hobby! Listen to your favorite lively song. So on and so forth. You get the idea,
A good Work/Study - Self - Family - Friends balance will surely help a person out!