I find finding exact reasons what I feel the way I feel, what I have taken on, from whom, etc is rarely clear cut. It could have been that, or it could have been some negative energy lurking around? Maybe there e.g. had been a relatively recent stick up at that petrol station? Also I find that often if I have very stressed and exhausted massage clients, I feel fatigues before they even show up, and sine most of them are not spiritual in any way I sometimes wonder if fatigue is a negative energy, or the lack of energy (or likely both is possible?)
If I get drained I make sure I especially affirm my connection to healthy Earth energies, ie grounding. It is not just a way to get rid of negative energy, but also to get fresh energies up.