Many people think they are doing their bodies a great service, by having a yearly... well, service... with a detox of a few days or a week at most. It sounds like a good idea in principle!
Assuming that you want to undertake a 7-day detox with a water fast, or juicing, or detox program pack from your chemist, or some other online detox method, I have some news for you - it won't work! You can't do a weekly detox and hope that it undoes all the damage and toxic accumulation from the previous 51 weeks of the year! It's not possible!
Also, what is it exactly that you want to detox?! Not actually knowing this is also setting up for failing in your detox. Short term detoxes are useless, but targeted detoxes that are tailored against specific toxins, organs or heavy metals CAN and DO work very well! The key is to know what toxins you may have and then setup a treatment plan for that. This can be done with a number of options for testing, such as with a HTMA (Hair Tissue Mineral Analysis) test, Oligoscan or other tests. I can help with these! I've seen some great improvements with targeted detox treatments, including those with high amounts of lead, mercury, aluminium or other toxins or heavy metals.
Many toxic chemicals from foods or household/cleaning/work products are stored in body fat as a "safe" and out of the way place. When you detox, you are generally on a diet, which is actually a restriction of nutrients (NOT a restriction of calories as such) that your body really needs. The reduced food intake will mean that body fat will be broken down to provide energy. That's all good for reducing your weight, but when you lose a reasonable amount of body fat, those stored toxins are also released into the blood. This is not a good thing, and it WILL make you feel worse. This is why you feel terrible on a detox program - you feel like your brain is fuzzy, aching all over, headaches, gut problems and fatigued... This is why you should never detox when you are sick or not feeling well - you will feel worse. And also why you need to support your body to detox when you are losing weight!
A non-specific detox for the body is a great idea, but this needs to be a part of a regular lifestyle, not something you do once or twice per year! It needs to be done all the time! A general detox can be done properly though without feeling terrible when you do it, with a regular and holistic program that covers all aspects of health - physical, mental, emotional, environmental and more.
Detoxing starts with an analysis of what you are normally eating and drinking, and what chemicals you are being exposed to. Then you should be making some changes to reduce your toxin exposure by replacing some items with safer and less toxic ones, and supporting the body's natural elimination channels to remove stored toxins.
So perhaps please reconsider your short term "detox" plans on your new years resolutions list! Replace it instead with aiming for a "healthy lifestyle" in 2019 instead, or using testing to find out what toxins your body has first, then use a targeted detox against those. I can help you with this!