IPL Laser Side Effects - When do They Go Away?

The descriptions of the scars are not entirely consistent with the shape of the Syneron handpiece (rectangular) or the rails. You may be having some pigment irregularity from past scarring and the IPL removed the pigment over the scar. Loose skin is not caused by any laser I know of. The pock like indentions can be treated with a fractional laser system by a reputable company and competent practitioners.

You mentioned several possible IPL side effects and so we will address each one independently.
1. Hyperpigmentation from Burns. Hyperpigmentation is a darkening of the skin caused by trauma. For light skin types this type of coloration normally goes away on it's own. If it persists for you, there are two options we use, hydroquinone bleaching cream and q-switched lasers. If using q-switched lasers, make sure the practitioner is extremely experienced as you are treating a trauma scar with more light, which can be tricky.
2. White Hypopigmented scars. There is no easy solution for this. We hope they will resolve on their own. If not, you may want to look into Excimer lasers. These are the lasers used to treat Vitiligo and they can help with repigmentation, but it is a slow (and many times temporary) process.
3. Pock Like indentations. Were you heavily scabbed after the burns? Are these pock marks in the same location as the burn? If so, they will probably not go away on their own and you may need to consider some form of laser resurfacing to help (Erbium, fractionated, etc).
4. Loose Skin. Did you have your neck treated? You only reference a facial treatment and not the neck. In any event, we do not know of a laser treatment that would cause the neck skin to loosen. Usually it would be the other way around with light based treatments improving skin laxity.