idk how to feel

     i really can't stop reflecting on every good moment i've ever had and feeling disappointed that I don't get to experience it anymore. it's super distressing and i keep trying to tell myself to cut it out but it feels a tad inevitable. even while the moment is occurring i already miss it, and then the memory feels permanently tainted by that thinking. i really don't know what to do, because every time i feel great, this longing feeling constantly reoccurs and i think its beginning to keep me up at night? okay, i know this is kinda a stupid tangent, and im not sure if anyone will reply... but do any of you guys also feel this way / have felt this way at a certain point in time and know how to prevent it? the answer might just be self control, but im not sure. please let me know!! love u and have a great day!!