No questions whatsoever

PS. I'm running low six minute mile but that's still beginner. I guess never really understood how most of the people were running ten milers at 6:30 pace for recovery.
I am keeping one long run a week though

PPS. But why, why did my mile went down significantly when I joined cross-country and pretty much forgot what fartlek is for two months? I did run my longer runs irregularly but I was never focusing on full out sprinting during them, just some accelarations. I mean, okay here's my history:
May: 7:40 mile
May-August -- fartlek intervals like you said. I did mile warm up, and one-two miles of running with 100-200m bursts as fast as I could and jogging (
really slow -- 12 minute mile pace) recovery.
August: my mile is 7:20 (O_o?)
August: I join XC and start running:
1. Long runs, which pretty much were tempos for me because I tried to run very fast for as much as I could keep up with the team. Then I just ran on what's left. Usually 5-6 miles.
2. VO2max -- 500m/900m intervals full out.
3. Some 5k races.
5. Easy three mile recoveries.
October: I run 7:03 mile.
Then I remember a couple of 3x900,4x400 workouts I did. But I still was running mainly long steady runs and tempos.
Then I took a break and jogged slowly/walked for two weeks. My mile is dropping to 6:45.
In November, I start running stuff like 5-6 miles consistently. I also started running 8 milers (which is new) and 6 mile tempos. XC season is long over by that time.
Then, here's how it went:
three days before this week I went 6:30 mile.
Week1: 4miler @ 7:30 pace, 1 suckish 8-minute mile, rest, 2.6+2 mile (double), 3.4+3, long 8 mile run.
Week2:
Monday off.
Tuesday: 5 mile progressive run: started in like 8 minutes, finished in 6:40.
Wednesday: 2 mile recovery
Thursday: 6:16 mile! So, basically I knocked down 40 seconds without ever doing any sprints or stuff like that.
I am scared to lay off the technique that worked wonders for me and switch to something that has done a terrible job for me. Maybe I am mutant or something?

The thing: I progressed fastest only when I ran long miles.
Another point: I went from 7:03 to 6:16 without running anything less than 1 mile.