The shorter your colon cleansing process, the stronger the side effects will be. Therefore, if you choose to go for a high colonic, you might have to face side effects like migraines, nausea, flu-like symptoms, cramps, diarrhea, body ache, fever and extreme exhaustion. Some people also experience nervous symptoms like depression, anxiety, irritability, panic attacks and weepiness. However, these side effects are short lived and are generally over within three to four days. If you choose to go for a colon cleansing program that takes one to two weeks or even more, then you might escape with just diarrhea, nausea and headaches which are generally caused because of electrolyte imbalance.