Yes it is possible to over insulate your home.
If you add too much insulation to your home then you can cause the house to be too tightly sealed up which prevents the house from properly breathing.
If the house doesn't breathe properly then moisture can build up in the home and lead to mold issues and also lower the indoor air quality as well.
So you just want to add the proper amount of insulation to the home to keep it cool in the summer and warm during the winter but don't add too much insulation because your house will likely suffer mold damage from the moisture problem.
And you could have health issues as well.
If you have old windows in your home they could be leaking out heat and cool air so by replacing the old windows with new replacement insulated windows then you'll save money on your heating and cooling costs and be more comfortable in your home.