Why is my plant falling over?
A plant that will not stand up has either lost its root anchorage or is reaching sideways for light.
The causes, and how to tell them apart
Root rot at the base most common
How to tell: Leaves are soft and yellowing at the soil line and pull away easily. The base is mushy.
What to do: Unpot, cut away all rotted tissue, repot the firm remainder into dry gritty mix, and water much less.
Reaching for light common
How to tell: Leaves lean consistently toward the window, stems are stretched and pale, but everything is firm and healthy.
What to do: Move it to brighter light and rotate it a quarter turn weekly.
Top-heavy or pot-bound common in tall plants
How to tell: Roots circling the bottom or emerging from the drainage holes, and the pot tips easily.
What to do: Repot one size up into a heavier pot, or stake it.
By species
The likely answer differs by plant — these species have their own version of this problem:
Plantroster compares this month's photo against last month's, so slow changes — the ones you stop noticing because you see the plant every day — get flagged.
Open PlantrosterOther problems
General horticultural guidance, not a diagnosis of your specific plant.