It's not uncommon for parents to grieve when they learn their child has special needs and won't be able to have the life they'd imagined.
Or if someone learns they have a disability or chronic illness themselves grief is a normal reaction.
As when someone dies, it's usual to go through the five stages of grief explained by Elizabeth Kubler-Ross (sorry I don't know how to add umlauts to her name.) Those stages are denial, anger, bargaining, depression, and acceptance and people may cycle through them for a long time or return to them long after they've come to terms with the situation. The same thing is true with the sort of grief I'm talking about, and any of the stages can re-occur at any time.
If they do, it's perfectly normal.