That’s pretty much how slots are designed to feel. The RTP (say 95–97%) doesn’t mean you’ll get that percentage back every session—it’s calculated over millions of spins. In the short run you can be way up or way down, but the longer you play, the closer you drift toward the house edge.
Casinos don’t need to secretly rig slots, the math already guarantees they win in the long term. The ‘hot start then slow drain’ pattern you noticed is super common because our brains remember the exciting wins and feel the losses more painfully. The only real way to walk away ahead is literally to… walk away while you’re ahead. 😅