Then it dawned on me...as I said in a previous post, when you get rid of something negative, you need to replace it with a positive. Otherwise you'll have a relapse. (And you can look to this fact for why going cold turkey, among other reasons, isn't really effective as well as why so many people "fall off the wagon" with various things.) When you get rid of something, particularly something you're use to having around, doing, or being you often leave a void. The longer you've had this a part of your life, the larger and more concrete the void is. And the easier it is to fall back into whatever bad habit you were trying to shake.
The same thing goes for energy. If you have negative feelings in your home eventually they start to grow there. While originally they may not have anything to do with you or your home life, like seeds being carried by a pollinator you track them into your space where they take root. Doing this over a period of time and you'll notice you have a "garden" of negative energy within your home. For those who are less obviously energetically sensitive you can notice this in other ways in the form of your home seeming to suddenly become cluttered physically, and through having bad feelings frequently while you're at home. (These apply if you already did not have these things going on.)
I often have people come to me asking about healing and feeling better and one of the first things I say to them is, "When was the last time you cleansed?" Most people are taken aback by this question as it is not something they considered would be any part of the problem. All too often it is one of the root causes. Like a media vampire, you've invited negative energy into your home and now, like a freeloader, it won't leave!
But, in serious cases, it's much deeper than that. What we address here is when you have realized this fact, started cleansing (over a reasonable period of time) and notice that while the air seems to clear, it comes right on back. Part of this is that with longer held thoughts and beliefs it takes longer to dispel them. You also need to look at whether you are consciously or unconsciously contributing to this negativity (this may take time and meditation to determine). But finally you need to realize that after you have cleansed, you need to invite positive energies into your space to continually displace the negative ones. Referring back to a course I participated in about "Raising Your Psychic Awareness" with Susan Hughes, I suggest burning Frankincense, Rose, or some other uplifting incense or oil after you've cleansed an area. Experiment with what you like and smells pleasant to you (as you will defeat the purpose if you can't stand how it smells while it's burning!)
While most of us within the healing community are taught the basics of cleansing, the need to uplift the energy afterwards is often not taught and then taken for granted. If you can't get ahold of a scent you can also try letting more natural light into you home or playing upbeat music. Whatever method you try be sure to hold the intention that this is what that action means - "you are raising the vibration of the space". After awhile you will consciously associate the actions with that thought and it will do the work for you.