I have similar episodes from time to time. For me, the only emotions that I truly understand tend to be the more unpleasant ones (fear, anger, etc), but the pleasant ones are typically elusive to me. Sometimes however, I do feel positive emotions and when that happens, I have a reaction that usually makes me revert to sadness (like breaking down hysterically in tears sadness). Sometimes, it's not that I feel sad, it's just that 1. I don't know how to process these emotions, and, 2. I have this subversive tendency in my personality to constantly feel like I don't deserve the good things that happen to me.
If it helps you, I've experienced much fewer of these episodes since I've started exercising regularly. If you are able to do so, I would definitely recommend that.
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Your Aspie score: 127 of 200
Your neurotypical (non-autistic) score: 79 of 200
You are very likely an Aspie