low calorie intake to normal calorie intake

Having been very sick about a month ago and having the same problem I would suggest adding about 200-300 calories a week. That would allow your body to adjust without getting sick. For me it was hard to add more than that without wanting to throw up. I did not gain any weight doing it this way.

I am sure there will be others that disagree with me, but it is what worked for me.

I would totally agree. Yes, you do want to take it a bit slowly so that your metabolism adjusts.

You should certainly consult a doctor, preferably an endocrinologist, who can monitor changes in hormonal function as well as Resting Metabolic Rate. If you were assuming a chronically restrictive diet for a very long time, your RMR may take a while to increase back to optimal levels. Eating too much too quickly may lead to more weight coming back if your RMR isn't given enough time to speed up. An endocrinologist I refer clients to normally recommends a weekly increase of around 100 calories and or an equal caloric decrease in activity - basically you need to gradually decrease the deficit you established and have been maintaining. Most of the weight gain you experience, though, comes from water weight so do not be alarmed if that happens.

Personally, if some of the weight you gain back is from actual fat, think of it as a small price to pay for the big picture - improving your metabolic and hormonal health so you can reach your weight loss goals in a more sustainable and healthy manner next time you set a more appropriate deficit. However, if you lost a reasonable amount of lean body mass from muscle, you may want to focus on strength-training at a surplus - once you reach your adjusted TDEE - to gain back what you likely lost.