After reading English Page’s Conditionals, I wonder how seriously natives speakers take the rules described in the articles. In the rules, there are 3 tenses: past, present, and future; 2 scenarios: real and unreal. It’s very hard for me to put the rules into practice.
I think what you need to remember is for native speakers these "rules" are completely intuitive. Most of us have never heard about the rules and yet we apply them routinely in our everyday lives.
Native speakers don't have to think to themselves: "Hmm, so I want to talk about an imagined conditional event that could have happened last week... hmm... Aha! I need to use such and such conditional form!". Absolutely not. We just intuitively know which form to use without even thinking about it.
Unfortunately, a non-native speaker cannot rely on this "deep-wired" intuitiveness. If you do intend to use conditionals in all forms you will have to learn them. There isn't any other way. You will not be able to communicate precisely otherwise.
For instance you could decide to ignore the rules and treat every conditional case as the Present Real Conditional. But if you do so you will not be able to talk about any event occurring in either the future or the past without a great deal of confusion. You also won't be able to talk about anything imaginary or hypothetical, again not without a lot of confusion.
So to answer your main question, no, native speakers aren't "serious" about using the right conditionals. Nobody will be offended (it's hard to be offended by something one doesn't know exists). We just won't be able to readily understand what you're trying to say.