I had two laser sessions on some nevi and six non-ablative laser sessions on post acne scars.  During treatment (6 months) I didn't apply sun block regularly.  It was about 200 hours collectively of exposure to indirect sunlight coming from the window when indoors, or in a car, fluorescent light, and some direct sunlight.  What are the risks of side effects?  Is there a risk of malignancy (in skin or nevi) due to exposing freshly lasered skin to sun during its healing, as laser treatments make skin more sun sensitive?

It is hard to say specifically.  Surface treatments remove some of the protective elements of the skin so you are a bit more sun sensitive which can lead to pigmentation and other aging changes.  I don't feel the non-ablative treatments will put your skin at the same increased risk but still may have an effect.  Cumulative sun exposure and "burning" can enhance your risk for malignancy. 

Laser treatments make the skin more sensitive to sunlight by removing the thick outer dead cell layer (one of the reasons the Laser is done).  The risk of not wearing sun block is the same as it is without the Laser, mainly sunburn, aging of the skin and development of skin cancer.  Whether you have had a Laser or not, you should wear a good UVA/UVB blocking sun block daily.  It is the UVB that causes sun burn, but it is UVA that causes aging and skin cancer.  UVA is present all the time (morning, noon, evening, summer, winter, North Dakota, south Florida) unlike UVB which is strongest down south, mid-day in the summer.  I suggest a sun block containing at least 5% clear zinc oxide as it lasts longer than Avobenzone and blocks both UVA and UVB.