Welcome. The paths of energy converting to matter and vice-versa are fairly well documented ... in particle physics. Your question about it being a frozen form of energy is hard to answer definitively because it seems to about something at a finer level of detail than we have theory to support. If String Theory (or something like it) gets worked out we might have answers ... or not.
Originally Posted by notayankeesfan
When two particles interact, there is a chance that they will change to lower mass particles and release energy in the form of photons (which maybe you'd consider to be particles also, but we rarely talk about photons as matter). Sometimes when two photons interact, if they have enough energy, they will give off a pair of particles, and the photons will have less energy of their own.
Forming opinions as we speak