One way to approach this is to alternate between standard freestyle and sidestroke--that way, you are a) teaching yourself gradually to tolerate the freestyle part, and b) allowing yourself to have planned breaks from it so you won't panic. Try a specific plan, like 8 strokes of freestyle, 8 side, etc., or whatever number might work for you.
"My predominant feeling is one of gratitude. I have loved and been loved;I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal, on this beautiful planet, and that in itself has been an enormous privilege and an adventure." O. Sacks