I'm a male, 37 years old, 5'10" and 194 pounds. I can't say exactly how long it's been happening but it's long enough that I feel like it isn't normal. I think the earliest I can possibly say it started was about 5 years ago, but before that I was dealing with constant fatigue from depression and medication. I'm currently working on a journal to try and get more ideas on how often they happen or what might be causing them.
The crashes themselves though, they will start slowly like I feel like I'm just getting tired and need to take a break. If I am working or doing something, they make it hard to socialize or get things done but I'm able to push through at least. If I sit down then they will sometimes hit so hard that I'm fighting to stay awake or if I lay down I will fall asleep and nothing is going to stop it. Since I started journaling about them and paying more attention, I notice they will last about an hour for milder ones and for 2-3 hours for more severe ones. There doesn't seem to be a consistency to them either. Sometimes a week or two will pass without one happening and sometimes they are happening every day or two.
I do have ADHD and take meds for it which seems to help a bit with them, more of them seem to be on the milder side when taking meds than without. Before meds the crashes could at times happen every day for weeks or even a month or more and would all be severe. I'm planning to see a doctor but I don't really have the best impression of doctors caring or taking it seriously.