There are no true side effects; that is, there are no long-term side effects.  Occasionally, some temporary discomfort may be experienced after the first or first few treatments.  The possibilities include headache and/or slight nausea if you have tissue toxicity.  It will quickly subside, do not be concerned.  In an injured area, you may possibly experience increased pain levels at first until the condition begins to resolve.  Fortunately, these side effects are rare and usually occur, if at all, following only the first one to three treatments, while your body is adjusting to an increased level of cellular self-repair activity.
GOOD NEWS!  Any change, including temporary increased discomfort is a good sign.  It shows that change is happening (and you must admit you could use a change!)  Almost everyone who feels some increase in discomfort immediately or soon after the first treatment or two has very good long-term pain-relief response.  For most people, the “side effects” are simply feeling better and better in various ways after each treatment.