not PPD but on the other side of the spectrum

I hear all this talk about postpartum depression but nothing about the other side of the spectrum. I am not a overbearing mother. I let my child experience stuff without me hovering.

it took me 3 years to get pregnant and my son is now 8 months old. I catch myself not accepting future milestones like turning 1 without getting emotional. Last night I was looking at the baby monitor and he was sleeping peacefully and I started crying to my husband saying one day we will not be here and he will be all alone. I don't think this is normal and I feel sa but not depressed. I am completely in love with him and attached to him so it's not so much depression but what is it.