This is a true incident, please check my grammar!

[new2grammar]

Yesterday after dinner, I went out for a stroll with my dog. I unlocked dog’s chain so he could roam freely and I was standing next to my car parked under a tree. I heard a voice as if something is cracking, very thin sound as if it is coming from very far away place. But then after a few seconds a huge branch of the tree fell just next to me, for a moment I didn’t realised what happened. But after coming to senses lots of horrifying images conjured up in my mind and it made me very afraid, if I had have been standing even an inch ahead that branch would have fell on my head and it would have hit me badly and injured me severely. I am really thankful to God that he saved me or else I would have been in hospital or may be strolling in the heaven!

[Soup]

Yesterday after dinner, I went out for a stroll with my dog. I unleashed the dog next to my car, which was parked under a tree, so [that] he could roam freely. I heard a faint sound as if something were cracking from a very far off place. A few seconds later, a huge tree branch fell right next to me. For a moment, I hadn't realised what had happened, but after coming to my senses, all these horrifying images just hit me and made me quite afraid. If I had been standing an inch closer, the branch would have fallen on my head and injured me severely. I am really thankful to God that He saved me. Otherwise I would have been in hospital or even strolling in the heaven!

[new2grammar]

Thanks Soup for your kind help. Can you just clear my little confusion, when to use fell or fallen?

[Soup]

Simple past tense: I fell this morning. <specific time>
Present perfect: I have fallen here before. <time is irrelevant; the event itself is the most important>