I did a 1000-calorie daily deficit for a few months, in order to lose two pounds a week. I got used to being hungry all the time after a couple of weeks, but having a lot less energy and being sleepy during the day were harder to deal with. My body was trying to conserve calories that way, but pushing through it was possible.

The hardest part was actually accurately counting the calories. It was relatively simple for off-the-shelf food, but a lot more annoying for things someone else home-cooked for me. I had to ask for the recipe every time, weigh how much I ate, and then track the calories per ingredient on a spreadsheet. Restaurant food was effectively impossible to count, but that didn't matter much because I was so focused on filling food that I wouldn't have eaten it anyway. I'm a vegetarian, so I ended up eating mostly beans, tofu (which is also beans, now that I think about it), and vegetables. Other things weren't as filling per calorie as those foods.