My kitten is super lethargic

Hello! So my kitten is a feral that was saved at about 16 weeks, she’s now about 6 months old and has only recently become friendly enough to touch and pet (over the last two weeks). She’s been super playful, cuddly, eating well, and everything seemed super normal. Yesterday, I noticed that she had hardly moved all day. She slept throughout the entire day in one spot, and only moved sparingly to eat a little and potty, then went back to bed. Today, more of the same, she will not walk around, she just wants to sleep. There are no other symptoms from what I can tell, her poops are fine, she’s not throwing up, she’s just been tired for 24 hours straight. Should she be taken to the vet immediately? Should I continue to monitor her?

Any help is appreciated