It's very common to not notice your home is out of level until its too late. A lot of structural damage will occur if the problem does not get addressed.
A few giveaways that your home is out of level is your doors may stop working properly. They wont latch anymore and may not even close all the way. After time like that your door hinges and door frame will start to warp, which couldn't be fixed with a relevel at that point. Another way to notice your place is out of level is your skirting around the outside of your house will start buckling in on itself. This being the situation your hurricane tie down strapping will become loose rendering useless. Serious damage such and your roof separating will happen if the ground gives way on both sides of the home. There is also small tell tell signs as well such as your grease is always going to one side of the skillet or cracks are showing up on the walls and ceiling. You don't need to be a professional to pick up on some of these hints but leave it to them to get the job done. If your still worried about your homes level and want to check yourself you can take a 4 foot level throughout your home to give you an idea. A lot of the time I get called to level a home I go under and notice other things such as leaks, rips and tears, animal problems.