Be worry, but not too much. Section 20, Article III of the 1987 Constitution provides, thus: "No person shall be imprisoned for debt or non-payment of a poll tax." Although there can be imprisonment involving debts in cases of B.P. 22, the Trust Receipts Law, Credit Cards, etc. Your case does not belong to any of the foregoing, anyway.
On the first hand, there is the so called Small Claims Law, wherein there is no need for the usual Court proceedings wherein you will hire a lawyer and it is the Regular Court that will take cognizant of the case. It is just a sort of a mediation proceedings. If the amount of debt does not exceed Php100,000.00 it falls under the coverage of such Small Claims Law.
The legal interest (for instance, on awards by the Court, obligations other than loan or borrowing of money or property, etc.) is now 6% per annum. But if it involves
forebearance (loan/borrow) of money, it is 12% per annum.
I heard from a lecturer in Civil Law, Atty. Teresita Cruz, last year, that in both instances (forebearance of money or otherwise) the interest is now 6% per annum.
The Court or Small Claims Law implementor might make a decision on such amount of interest, aside from the principal or damages/Attorney's fees. But take note that under the Small Claims Law you need not hire a lawyer. If you undergo through the proceedings under the Katarungang Pambarangay, on the other hand, lawyers are not allowed to appear, so you need not pay for the services of a lawyer, neither will the creditor.
The following matters might no longer apply to your situation. But they might be informative even to other debtors and creditors as well. The collection of debt prescribes in 5 years. There must be a formal demand within that 5-year period. Otherwise, the creditor loses his right to collect the debt. Some collectors are hesitant to make a formal demand letter, especially if they have no license to operate a lending business. If the amount involved is too small they will just abandon the debt. But if it is big (for instance, it exceeds Php100,000.00) they have to file a case in Court. But the interest will be limited to 6% per annum. They might also pay for the services of a lawyer. On the other hand, it might not be practicable for the Court to be awarding Attorney's fees (This is not supposed to be an award to the Attorney by the winning litigant but this is an award to the winning party, in the form of damages payable by the losing party.) I heard recently that the so called five six scheme of lending money is illegal. I even heard that warrantless arrest might apply against the collectors like the typical Bombay. Warrantless arrest means that a citizen ('s arrest) can effect an arrest under Rule 113 of the Rules of Court, when in his presence, a crime has been committed, actually being committed or the person to be arrested is attempting to commit it.
By the way, borrowing money with the intent not to pay it should never be made a habit. No one is imprisoned for non-payment of debt but a debtor can get killed for non-payment of debt. Imagine what kind of face a debtor can show to a creditor whom he has never paid. Life is just like a wheel. there might also come a time that one's finances would improve and he now has capability to pay his debt. "A debt never grows old for an honest man to pay."
I hope I have shed light on your legal question.
NOTE: I am not yet a lawyer. I am yet to take the Bar this coming November this Year. Please consult other legal minds, preferably from the Public Attorney's Office. It appears that you are not in a position to hire a Lawyer because the amount involved is too minimal.