Another important feature of this kind of loan is that the "adjustment" periods are capped (often at 2%).
The adjustment period occurs after the 5 yr fixed period is up. This would mean that after 5 years, the most it could increase would be 2% for year #6.
Now, this can vary depending on the loan, so please check with your lender.
There (usually) is a "lifetime" cap (often 5%) which limits how high, in total, the loan can go after the fixed period is up.
If a loan started at, for example, 4% and has a life time cap of 5% - that means, in the worst case scenario, the rate can go up to a max of 9% .