I feel like a burden every time I need support from friends

My friend asked how I was doing and I almost said the truth — that I've been barely holding it together — but I smiled and said 'fine, just tired.' I didn't want to dump on her when she's dealing with her own stuff. This happens every single time. I end up minimizing everything until I explode over something tiny. I hate that my default is assuming I'm too much for people. Does anyone else cancel plans or downplay things because you feel like a burden?