Mortgage is “a conveyance of an interest in property as security for the repayment of money borrowed” (wordreference.com).
As you can see in the definition, interest is conveyed through mortgage. Dealing with interest is one of the most important prohibitions in the Quran:
“Those who consume interest behave no differently than they who the Devil has confounded with his touch. That is because they say, “trade is equivalent to (gaining) interest.” God has made trade lawful and has forbidden transactions with interest. So, whoever has received an admonition from his Master and discontinues (dealing with) interest, what was received in the past belongs to them. God undertakes their affair (about the past interest income), but whoever resumes (dealing with interest) is a resident of the Fire. Therein they will abide as immortal.
God causes the business practicing interest to depress and the business practicing the zakat/the alms to grow. God does not love any of the sinners who are obstinate (about dealing in interest).” (Al-Baqarah 2:275-276)
Nobody loans without necessity. The important thing is avoiding to deal with interest even though you are in necessity. This is why you don’t feel relieved. Our prophet (p.b.u.h.) explained this measurement to Wabisa as follows:
“Wabisa, consult your heart, consult yourself! Goodness is what your heart finds peace in and what yourself finds peace in. Sin is what disturbs the heart, the thing that wanders around in chest, even though people had given you a fatwa or had found the thing that you do acceptable.” (Sunan Al-Darimi, Buying&Selling’, 2; Ahmad bin Hanbal, 4/228)